Outdoor recreational activity experiences improve psychological wellbeing of military veterans with post-traumatic stress disorder: Positive findings from a pilot study and a randomised controlled trial.

TRIAL REGISTRATION: The authors confirm that all ongoing and related trials for this intervention are registered. The studies reported in this manuscript are registered as clinical trials at ISRCTN: Pilot ID- ISRCTN15325073 RCT ID- ISRCTN59395217.

RCT Entities:   Population Interventions Outcomes

Introduction

Post-traumatic stress disorder (PTSD: DSM-5 [1]) is a disabling psychological condition comprising four main sets of symptoms: re-experiencing, hyperarousal, avoidance and negative changes in thoughts and mood. Re-experiencing refers to intrusive thoughts or images, flashbacks and/or nightmares. Hyper-arousal may be characterised by sleep disturbance, irritability, anger and hyper-vigilance for threat in the environment. People with PTSD tend to cope by avoidance of situations and social interactions and have difficulty in regulating emotions. Social maladjustment, phobia, anger, violent behaviour and family discord are often associated with combat-related PTSD [2]. PTSD is also frequently comorbid with other mental health problems such as depression, anxiety, substance abuse and suicidal ideation [3, 4]. If left untreated, PTSD may become a chronically disabling condition associated with impaired occupational, relational and social functioning [5].

It is notoriously difficult to estimate the numbers of military veterans with PTSD. A comprehensive review of evidence from multiple sources [6] suggests a prevalence of between 2–17% amongst US veterans and 3–6% of UK veterans, with estimated rates affected by a range of methodological factors such as sampling strategy, measures, criteria employed to determine cases, as well as combat role and cultural background. Given that, in the UK for example, there are more than one million military veterans aged 20–69 [7], and in the US approximately 20.1 million [8], these percentages translate into substantial numbers of men and women living with a condition that impacts upon their wellbeing and life quality, capacity to work, maintain personal and parental relationships and social connectedness, all of which incur substantial personal and public costs. While established evidence based psychological treatments exist for PTSD [e.g. 9], evidence suggests that military veterans with PTSD in particular do not benefit adequately from such provision. The present paper reports upon the rationale, development and evaluation of a supplemental outdoor recreational experience approach to reach UK military veterans with PTSD.

Limitations of existing treatment for military veterans with PTSD

Studies have found that large proportions of veterans with mental health problems do not receive any mental health treatment [10-12]. Hoge et al. [10] report that only 23–40% of veterans with health disorders had sought treatment. Kuehn [11] reports that more than 45% of US military veterans with PTSD who were referred for treatment never received any form of therapy. There is also evidence of significant delay in treatment seeking; Murphy [3] reports that veterans may experience mental health difficulties for as long as 12 years after leaving service before seeking help. Literature indicates that three significant issues impact upon the ability of military veterans to benefit from standard provision of treatment for PTSD. These relate to barriers to enter or remain engaged in treatment, reduced effectiveness of treatment and comorbidity of PTSD with other conditions.

Barriers to enter treatment have been extensively documented and include beliefs about mental health treatments, perceived stigma and access barriers [13-17]. Mellotte et al. [18] distinguished between barriers to enter treatment and barriers to progression through treatment in UK veterans. Barriers to treatment entry included minimizing or not recognizing that symptoms were psychological as opposed to physical, shame and embarrassment, anticipated negative judgements from others, including fear of being perceived as weak or malingering by civilians. Barriers to progression through treatment once initiated were more concerned with service delivery; lengthy waiting times, difficulties with coping with busy public transport services, and health professionals who lacked necessary military specific knowledge and terminology. All participants who sought help did so only when they reached a crisis and risked losing their life, liberty, family or job. There is also evidence that established psychological therapies may be less effective and terminated prematurely by military veterans [19, 20]. In their meta analytic review of effects of cognitive behaviour therapy and eye movement desensitization in treatment of PTSD, Bradley et al. [21] obtained an aggregate effect size for treatment of combat trauma that was less than half that obtained in the treatment of other traumas. The authors suggest that one important factor is the tendency to limit disclosure at home (to civilians) so that engagement in ‘homework’ is limited and participants consequently do not avail of important social support during therapy. Comorbidity also complicates treatment [3, 4, 22] and extreme avoidance, anger reactions and loss of hope may also contribute to early departures from treatment. In sum, various lines of evidence point to the need for innovative approaches to overcome the barriers to mental health care amongst military veterans.

An alternative approach: Outdoor recreation experiences

A developing body of evidence points to the positive impact of exposure to natural environments on psychological wellbeing in general populations. Several reviews [e.g. 23–26] suggest that exposure to nature and outdoor recreation can improve attention and cognition, memory, stress and anxiety, sleep and quality of life. Natural environment exposure is thought to benefit wellbeing via a number of mechanisms; at the forefront of these is attention restoration theory [27]. Attention restoration theory suggests that one’s environment can influence cognition and behaviour in terms of workload and induced fatigue. Specifically, urban environments require directed attention and increased processing of stimuli, thereby increasing cognitive load and fatigue. In contrast, natural environments require less directed attention, eliciting more putative ‘soft fascination’ compared to the ‘hard fascination’ that tends to occur in urban environments. This soft fascination allows involuntary attention and aids recovery from fatigue.

In recent years researchers have begun to explore the possibility that outdoor recreational activity experiences may have therapeutic benefit to military veterans with PTSD. Outdoor recreational experiences have attracted a multitude of labels including ‘green exercise’ [23, 28], ‘therapeutic recreation’ [29], ‘forest bathing’ [30] ‘peer outdoor support therapy’ [31], ‘nature adventure rehabilitation’ [32], ‘nature based therapy’ [33] and ‘nature recreation experience’ [34]. These interventions often combine the benefits of a natural environment with learning a new recreational skill from certified professionals.

Greer and Vin-Raviv [35] identified 13 articles, all but one published since 2011, providing a quantitative (n = 9) or qualitative (n = 4) evaluation of some form of outdoor recreation-based intervention offered to military veterans with PTSD. The majority were conducted in the USA, one in Israel and one in Denmark. The type of recreation offered by professional instructors included horticulture, sailing, fly-fishing, surfing, hiking and snow sports delivered to small groups of veterans, and ranging in duration and intensity from two days [e.g. 36] to once weekly for twelve months [32, 36]. The focus of these interventions, rather than being the active treatment of PTSD, is on learning a new recreational skill, thereby avoiding elements of shame or stigma and known barriers to therapy in this sub-population. In learning a new skill, participants may be distracted from everyday concerns whilst engaged in the task at hand and have an opportunity to practise problem solving, and solution rather than avoidant coping modes to overcome difficulties. This is important because chronic PTSD clients often minimize their interactions with the environment and with people, rarely encountering real life challenges [32]. Success and enjoyment in learning a new skill may address hope and facilitate development of a sense of identity and purpose beyond PTSD and the military. Frequent breaks between bouts of activity and passivity may foster experience of natural cycles of emotional regulation. Importantly, the natural environment provides a break from constant hypervigilance and reactivity to sudden sensory inputs and induces relaxation [33, 37]. It has also been suggested that natural environments per se, may represent calm and familiarity to veterans because of the many hours spent training in natural environments [38]. A third important element of these interventions is that they involve small groups of military veterans with PTSD. Peer groups have been observed to have great therapeutic potential [31]. Groups of veterans have the potential to recreate an ‘esprit de corps’ that strengthens belonging and may develop a social network that facilitates sharing of tips such as how to handle particular situations [32]. Mellotte and Murphy [18] observed that discomfort when speaking to civilians was a factor in discontinuation of treatment. Peer groups may also facilitate a feeling of safety as a consequence of being amongst veterans facing common challenges, who share a common language and understanding. In sum, outdoor therapeutic recreation comprises three important elements; being in an outdoor natural environment, being amongst other veterans and professional instruction in a new recreational activity.

Evidence from this evolving literature to date suggests that interventions that incorporate these three elements have had some success in demonstrating statistically significant pre- to post-intervention changes in PTSD symptomology [29, 32, 36, 39–41] and depression [29, 32, 36, 39, 41, 42]. However, few studies followed up post-intervention [e.g. 36] and some studies found that improvements were not sustained post intervention [e.g. 29, 41]. To date, only two studies have employed a comparison group. Hyer [43] employed a quasi-experimental design in an evaluation of a 5-day outward bound experience including a range of activities including ropes, climbing, hiking and white water rafting. No difference was obtained between the intervention and comparison group at the end of the intervention. Gelkopf [32] evaluated a 12-month programme involving 3 hours of sailing per week. Participants randomly allocated to the intervention or waitlist control group were significantly different in PTSD symptoms, daily functioning, hope and depression at the end of the programme.

The present studies

The present studies added to the developing literature in outdoor therapeutic recreation for military veterans, by conducting studies amongst British military veterans with PTSD. These studies extend previous literature in a number of respects. We compared three different outdoor recreational activities that were available locally. Previous research has explored a multitude of recreational activities, many provided in rather exotic and stunning locations far from participants’ homes, such as Green River Utah or the Appalachian Trail [e.g. 36, 40, 42–44]. We developed and tested an intervention that could be delivered close to veterans’ homes and represent minimal practical access difficulties to veterans. This intervention could be readily delivered in many locations in many parts of the world. We sought to discover if these activities and contexts might produce results similar to those obtained in more dramatic natural environments. Moreover, we considered that a locally delivered intervention might enhance possibilities for subsequent social support from other veterans taking part. We also sought to address some limitations of previous research. First, we excluded all potential participants who were in receipt of psychotherapy. Military veterans often avoid psychotherapeutic treatment for many years, and as noted by Gelpkof [32], interventions such as these may be particularly valuable for those not yet ready to engage, who have not benefitted or who have been treatment drop-outs. Also, the inclusion of participants who were concurrently receiving psychotherapy in some previous studies [e.g. 40] makes it difficult to discern if benefit arose from the novel intervention or from ongoing psychotherapy. Second, only two previous studies have attempted a control comparison [35]. Consequently, after estimating the effect sizes obtained in our first experiment we conducted a power analysis and conducted a controlled experiment with random allocation to experimental condition in our second experiment.

Aims

We designed two experiments to contribute to and extend previous literature by providing an evaluation of the effects of brief peer group outdoor recreational activity experiences and the potential for military veterans to engage in such interventions. The two experiments employed different samples of military veterans with PTSD in the UK. The experimental interventions were targeted at military veterans with PTSD diagnoses who were not in receipt of psychological therapy. An outdoor recreational experience was provided and led by professional coaches. A procedure was developed for the delivery of the intervention to ensure replicability. The first experiment compared three different types of outdoor experience (angling, equine care, falconry/archery) and employed a within participant design with follow up at 2 weeks and 4 months. It was hypothesized that participants would experience a decrease in symptoms as assessed by established measures of PTSD, depression, anxiety and perceived stress as a consequence of the experience. Encouraged by the findings of experiment one, we conducted a waitlist-controlled experiment (angling: experiment two) to compare the effect of the experience with a control group. The hypotheses that experimental participants would experience a decrease in symptoms of PTSD, depression, anxiety and perceived stress and an improvement in ratings of general social functioning and psychological growth, relative to controls, were supported.

Ethical approval statement

The University faculty ethical review committee granted approval for the experiments. A health and safety risk assessment was also completed and fully trained professional coaches and a high intensity psychological therapist were present during the experiments. Participants were volunteers who gave written consent to take part in the experiments. They were informed that all co-participants would be military veterans with the same diagnosis and that a mental health professional was on site as well as professional angling/riding/falconry coaches. The authors confirm that all ongoing and related trials for this intervention are registered (IDs: ISRCTN15325073 and ISRCTN59395217).

Experiment one

Method

The studies reported in this manuscript were approved by the University of Essex Ethics Committee (ethics ID: MW1501/2). All participants gave informed written consent before taking part in the studies.

Design and participants

The experiment employed a pretest-posttest within participant design (time: pre-intervention, 2 weeks post-intervention, 4 months post-intervention) with one between groups factor (type of activity: angling, equine, falconry and archery combined). Each activity intervention was designed to deliver an outdoor recreational activity in a peer group context and to facilitate opportunities to socialise and to discuss military experience or PTSD experience if the participant so wished. The three different activity interventions ran sequentially and employed the same eligibility criteria, recruitment process and evaluation.

The experiments took place in the environs of a super-garrison town in the UK. Participants were recruited from a population of 65 service users registered at a local military welfare service (Veterans First). The service provides a social coffee morning where veterans and their families can meet up. There are representatives from military charities in attendance, who can address any questions the veterans may have. The service consented 30 willing volunteers (25 men and 5 women) who met the eligibility criteria: military veteran with a formal diagnosis of PTSD by a National Health Service or Ministry of Defence psychiatrist. Diagnosis was confirmed through documents showing a formal diagnosis by a psychiatrist presented by the participants to Veterans First. Definition of the term military veteran differs between countries. In the UK, the term ‘military veteran’ applies to anyone person “who has performed military service for at least one day and drawn a day’s pay” [45; pg. 2]; however, all our participants had served in the military for considerably longer (mean length of 11 years (SD 6.12)). No participant was currently receiving psychological therapy for PTSD. Participants were randomly allocated (using an online randomisation tool– www.random.org) to either an angling, equine husbandry or falconry and archery combined recreational experience.

A summary of participant characteristics (including service length) is shown in the left-hand portion of Table 1. The majority of participants were unemployed, taking prescribed psychotropic mediation and had left military service on average 11 years previously. Participants were informed that they would be provided with the opportunity to learn a new recreational activity from qualified specialists, connect with other veterans with PTSD who share similar life challenges, and enjoy the setting. Recruitment began in August 2014 and data collection continued until June 2015 (4-month follow-up). All screening and data collection was carried out via telephone interview by a research assistant.

Table 1

Summary of participant characteristics, Experiments 1 and 2.

	Experiment One				Experiment Two
	Total	Angling	Equine	Falconry	Total	Intervention	Wait List
	N = 30	N = 11	N = 8	N = 11	N = 18	N = 9	N = 9
No. (%) men	25 (83%)	10	5	10	17 (94%)	8	9
Mean age (SD)	42.3 (9.1)	38 (8.9)	41 (7.8)	48 (10.7)	40.00 (12.70)	41 (13.47)	38 (12.56)
Years’ military Service (SD)	11.0 (6.12)	9.18 (4.45)	10.06 (6.62)	13.77 (7.30)	10.06 (5.33)	9.33 (4.06)	10.78 (6.53)
Years since leaving service (SD)	11.04 (9.47)	8.36 (8.04)	10.13 (9.34)	14.64 (11.04)	12.39 (10.84)	14.11 (10.98)	10.67 (11.06)
N (%) not employed	22 (73%)	5	8	9	8 (44%)	4	4
N (%) taking psychotropic medication	24 (80%)	8	7	9	14 (78%)	7	7

Intervention description

Each intervention was designed to deliver a day-long outdoor recreational experience involving tuition in a peer group context. Attention was given to creating opportunities for participants to interact with each other. In each context, the venue was made available exclusively to the veterans for the duration of the experience. Professional coaches (in angling, horse husbandry and riding, falconry and archery) provided instruction and were available at a ratio of two participants to one coach. A description of the coaching provision and activities undertaken in each intervention can be seen in Table 2 below.

Table 2

Coaching provision and idiosyncratic and common activities for all three interventions in Experiment 1 (see text below for common activities).

Intervention	Coach Provision	Distinctive Activities	Common Activities
Equine Husbandry	5 riding instructors supplied by the stables	Mucking out stables, feeding and grooming of horses. Horseback riding led by instructors	Minibus transportation.
			Health and safety briefing.
			Collaborative creation of a communal area for food and hot drink preparation by the veterans.
			Communal meals.
Falconry & Archery	4 raptor handlers and qualified archery coaches	Flying the birds to glove, feeding birds, cleaning aviaries. Target practice, then competition in archery	Minibus transportation.
			Health and safety briefing.
			Collaborative creation of a communal area for food and hot drink preparation by the veterans.
			Communal meals.
Angling	5 professional anglers were provided by the bait company some of whom also had level 1 or 2 angling coach certification from the Angling Trust, UK	Learning of angling skills and techniques, including mastery of rig tying, bait application and fish care	Minibus transportation.
			Health and safety briefing.
			Collaborative creation of a communal area for food and hot drink preparation by the veterans.
			Communal meals.

In addition to the different activities pursued, each outdoor activity experience contained the same common elements. Participants were transported to the venue by minibus. On arrival at the venue, a health and safety briefing took place. Participants were then allocated to coaches and provided with equipment (and designated horse in the case of equine, and designated fishing spot around a lake in the case of angling). Participants collaborated in setting up a communal area for the purpose of socialising, eating and taking warm drink breaks. Food (e.g. sausages, burgers, chicken, salad etc.) was provided to be prepared, cooked and shared by participants communally. The focus was on the recreational activity led by qualified coaches in a natural environment alongside veteran peers. At the end of the experience participants were encouraged to create a ‘Facebook’ group in order to keep in contact via social media. At the end of the day, participants were transported home by minibus.

A qualified mental health professional was on site throughout to observe and monitor signs of distress, and if necessary to assist any participant who experienced flashbacks during the experience, but no formal psychological therapy was offered or delivered during the intervention and there was no deliberate initiation of discussions relating to trauma. The mental health professional did respond to questions about PTSD and provided some basic information and signposting to appropriate services if approached.

The angling context provided participants with tents and tackle situated around a lake. Participants were free to move around the lake and talk to other participants. The equine context involved participants collaborating in pairs to groom, ‘muck out’, prepare food and bedding and clean tack for their own horses. They were then taught riding skills before embarking on a horseback walk in surrounding fields. The falconry and archery context provided participants with a half-day falconry and a half-day archery in two groups of 5 and 4 who swapped at lunchtime. Participants learned how to handle and fly raptors and were coached in archery.

Measures

Repeated measures were taken at three time points: two weeks prior to intervention(baseline), two weeks post intervention, and four months post intervention (see Fig 1). The researcher collected all measures by telephone. Four established and validated measures were included to assess mental health. PTSD symptoms were assessed by the PTSD Checklist Military (PCL-M; [46]). The Posttraumatic Stress Disorder Checklist is a commonly used measure, with military (PCL-M), civilian (PCL-C), and specific trauma (PCL-S) versions. The PCL shows good temporal stability, internal consistency, test-retest reliability, and convergent validity [47]. PCL-M scores range from 17–85; cut-off scores between 30–35 are indicative of PTSD for those in the general population and for those in Veteran Association Primary Care services cut-off scores between 36–44 are recommended [45]. Depression was assessed by the Patient Health Questionnaire (PHQ-9) [48]. The PHQ-9 has demonstrated reliability, convergent/discriminant validity, and responsiveness to change [49, 50]. PHQ-9 scores range from 0–27; mild, moderate, moderately severe and severe depression are measured with scores of 5–9, 10–14, 15–19 and 20–27 respectively. Anxiety was assessed by the General Anxiety Disorder (GAD-7) [51]. The GAD-7 has excellent reliability and validity [52, 53]. GAD-7 scores range from 0 to 21; mild, moderate and severe anxiety are measures with scores of 5–9, 10–14 and 15–21 respectively. Perceived stress was assessed by the 10-item Perceived Stress Scale (PSS) [54]. The Perceived Stress Scale exhibits good reliability and convergent validity [55]. PSS scores range from 0 to 40; with low stress categorised as being in the 0–13 range, moderate stress in the 14–26 range, and high perceived stress in the 27–40 range.

Fig 1

Summary of measurement and intervention timepoints for angling, equine husbandry and archery/falconry groups.

Results and discussion

All participants completed their assigned intervention, with no early departures. At the end of the first of the three sequentially run interventions, participants voluntarily created a Facebook group page to maintain newly established group connections. At the end of subsequent interventions, the participants were made aware of the Facebook group, and encouraged to access it.

Change in psychological wellbeing

Participants’ mean psychological wellbeing before the intervention and at 2 weeks and 4 months after for each activity type are summarised in Table 3. In order to assess the hypothesised change in psychological wellbeing from before to after the experience, a mixed MANOVA with one between groups factor (intervention type: angling, equine, falconry) and one within-participant factor (3 time points: two weeks pre-intervention, 2 weeks’ post intervention and 4 months post-intervention) was conducted on all four measures of psychological wellbeing. It was hypothesised that the analysis would reveal a significant within-participant effect. A Greenhouse-Geisser correction was applied to the within participant degrees of freedom whenever the Mauchly’s test of significance was significant, in both experiment one and experiment two.

Table 3

Experiment one: Summary of measures by activity group and measurement timepoint: Pairwise t-values, Cohen’s d and 95% confidence intervals for change in wellbeing over time.

Intervention Activity	Measure	M/SD 2 Weeks Prior	M/SD 2 Weeks Post	M/SD 4 Months Post	Pairwise t Prior/2wk post	Pairwise t Prior/4mth post
					t (d [95% CI])	t (d [95% CI])
Angling	PTSD	42.36/14.05	25.64/9.32	28.09/11.22	4.27 (-1.126 [-2.03, -0.23])	3.2 (- 0.878 [-1.75, -0.003])
n = 11	Depression	15.27/6.0	9.45/5.30	10.82/4.56	3.05 (-0.87 [-1.74, 0.005])	1.83 (-0.331 [-1.17, 0.51])
	Anxiety	13.09/5.91	10.09/5.24	10.64/2.58	2.53 (-0.58 [-1.432, -0.27])	1.33 (-0.316 [-1.16, 0.53])
	Stress	25.45/6.76	16.36/8.52	18.91/5.66	2.9 (-0.997 [-1.8, -0.11])	2.49 (-0.582 [-1.58, -0.14])
Equine	PTSD	42.38/15.61	32.25/14.28	36.13/17.02	1.75 (-0.595 [-1.60, 0.41])	1.19 (-0.44 [-1.43, 0.55])
n = 8	Depression	16.63/5.88	12.88/8.68	14.0/6.63	2.33 (-1.265 [-2.34, -0.19])	3.28 (-1.313 [-2.40, -0.23])
	Anxiety	14.00/5.83	9.63/7.50	11.63/5.73	2.43 (-1.03 [-2.07, - 0.01])	1.90 (-0.663 [-1.67, 0.34])
	Stress	25.63/8.18	19.13/9.66	20.63/8.85	3.92 (-1.59 [-2.71, -0.47])	3.99 (-1.491 [-2.60, -0.38])
Falconry	PTSD	41.36/9.65	28.09/12.75	28.73/11.84	4.10 (-1.485 [-2.43, -0.51])	4.09 (-1.395 [-2.33, -0.46])
n = 11	Depression	14.91/5.72	10.09/5.3	10.00/4.73	3.95 (-1.153 [-2.06, -0.25])	3.63 (-1.022 [-1.91, -0.13])
	Anxiety	12.27/3.64	8.91/4.46	9.00/3.87	2.06 (-0.695 [-1.56, 0.17])	2.27 (-0.707 [-1.57, 0.16])
	Stress	22.82/7.04	15.45/9.5	16.45/9.08	4.02 (-1.544 [-2.50, -0.59])	3.94 (-1.46 [-2.41, -0.52])
TOTAL	PTSD	42.00/12.62	28.30/11.93	30.47/13.18	5.76 (-1.026[-1.56, -0.49])	4.76 (-0.888 [-1.42, -0.36])
N = 30	Depression	15.50/5.70	10.60/6.28	11.37/5.32	5.35 (-1.033 [-1.57, -0.50])	4.03 (-0.71 [-1.23, -0.19])
	Anxiety	13.03/5.03	9.17/5.75	10.30/4.07	4.16 (-0.818 [-1.35, -0.29])	3.06 (-0.512 [-1.03, 0.002])
	Stress	24.53/7.12	16.77/9.00	18.53/7.87	5.67 (-1.199 [-1.75, - 0.65])	5.33 (-1.03 [-1.57, -0.49])

Results revealed the important significant multivariate within-participant effect reflecting change in psychological measures across time as hypothesized (F (8, 20) = 4.477, p = .003, partial eta2 = .642). The main effect of intervention group was non-significant (F (8, 50) = .470, p = .872, partial eta2 = .070), and the interaction of group x time was also non-significant (F (16, 42) = .420, p = .969, partial eta2 = .138) indicating that change across time did not vary significantly by activity type. Inspection of the within participant univariate F values confirmed significant reduction across time on all four measures. A Greenhouse-Geisser correction was applied to the degrees of freedom for PTSD and stress measures: (F (1.481, 39.997) = 22.057, p < .001, partial eta2 = .450 (PTSD symptoms)); (F (2, 54) = 15.356, p < .001, partial eta2 = .363 (depression)); (F (2,54) = 10.170, p < .001, partial eta2 = .274 (anxiety); F (1.417, 38.248) = 24.365, p < .001, partial eta2 = .474 (stress)). Means, standard deviations, pairwise t-values for the comparison of pre-intervention measures with two week and four month follow-up and Cohen’s d (1992) effect sizes and confidence intervals for each intervention are summarised in Table 3. Effect sizes were calculated according to Lenhard & Lenhard [56]. Significant reduction in PTSD symptoms was observed at two-week follow up that was largely sustained at 4 months. Effect sizes were medium to large. A post hoc sensitivity analysis conducted with Gpower 3.9.2 with alpha = 0.05 and power = .80 for a within-participant mean comparison indicated that a sample of 30 participants was sufficient to detect a medium effect (dz = 0.46).

Clinically significant and reliable change in PTSD symptoms

While statistical significance provides one index of change, it is also worthwhile to consider if the changes in PTSD symptoms observed might be considered clinically significant or reliable. For Clinically Significant Change (CSC) to be achieved, the level of functioning subsequent to the intervention should fall outside the range of the dysfunctional population, where range is seen as extending to two standard deviations beyond (in the direction of functionality) the mean of the population. The Reliable Change Index (RCI) is calculated using the change in a client’s score divided by the standard error of the difference for the measure(s) being used. The Cronbach’s alpha used within this calculation was 0.94, which was taken from Sutker, Davis, Uddo and Ditta [57]. Jacobson and Truax [58] provide criteria by which both reliable and clinically significant change can be identified. Where normative data are available for both clinical and non-clinical populations it is advisable to use this criterion (Criterion C) to calculate CSC. For the PCL-M, clinical (mean 63.6, standard deviation 14.1) and non-clinical norms (mean 34.4, standard deviation 14.1) were taken from Weathers et al. [46]. Data for all participants were included in two analyses: baseline-2 weeks post and baseline-4 month follow-up. The pre and post intervention PTSD scores for all 30 participants are illustrated in Fig 2.

Fig 2

Reliable and clinically significant change in PTSD symptoms (using Criterion C for PCL-M) at 2 weeks follow up, study one.

(N = 30).

When all 30 participants were included in the baseline-2 weeks post analysis 18 (60%) made reliable improvement; 11 (37%) made no reliable change; and only 1 (.03%) deteriorated. In terms of clinical significance 17 (57%) made a clinically significant change in relation to PTSD symptoms. Further to the analysis of the whole sample, an additional analysis of clinically significant change was conducted in which participants who at baseline scored below the clinically significant cut-off score of 41.80 (calculated using Criterion C) on the PCL-M were excluded from the analysis on the basis that if they were not scoring in the dysfunctional range for PTSD diagnosis at baseline it was not possible to make a clinically significant change post-intervention (i.e. move from the clinical range into the non-clinical range). At baseline, 12 participants scored below the clinical cut-off. Of the remaining 18 participants, 14 made clinically significant changes. Fig 2 illustrates the reliable and clinically significant change in PTSD observed.

For the baseline- 4-month follow-up analysis, when all 30 participants were included in the calculation of reliable change 18 (60%) made reliable improvement; 11 (37%) made no reliable change; and only 1 (.03%) deteriorated. For CSC, 16 (53%) achieved clinically significant change in their PTSD symptom score. After excluding those that scored below the clinical cut-off at baseline, 13 met the criteria for making clinically significant change in PTSD symptom scores.

In sum, findings from experiment one provide evidence that brief outdoor recreational experiences for groups of military veterans improve psychological symptoms. Moreover, our employment of a 4 month follow-up shows that effects were sustained over time. No significant interaction of group by time was obtained between the three groups in the multivariate analysis, indicating that the impact of the experience was not a function of the particular activity undertaken. Nonetheless, the experiment lacked an experimental control group. We therefore conducted a second experiment utilising a waitlist control group. The second experiment compared the effect of an angling intervention with a waitlist control group. Angling was chosen as it is an appealing pastime for our target participants and is a readily accessible and relatively inexpensive hobby to pursue should participants wish to continue after their intervention.

Experiment two

Design and sample size calculation

Experiment 2 was a waitlist controlled randomized experiment with two independent groups. Ethical considerations meant that it was not possible to have the waitlist group ‘wait’ until a four-month follow-up was completed for the intervention group (a wait of 18 weeks after recruitment). The controlled comparison of the angling intervention group and the waitlist group therefore is restricted to the two-week follow-up period. Results from experiment one were used to inform the sample size calculation. In the experiment one angling group, the effect of the intervention over time was large when we compared PTSD symptoms before and two weeks after the intervention (d = -1.126, 95% CI [-2.03, -0.23], Table 3), (correlation between within-subject measures, r = .44). Based on the effect of the angling intervention on the average of self-report PTSD symptoms, we computed the required sample size to replicate the effect in a between-participants design where we would compare participants’ PTSD symptoms in the intervention group and a control (wait list) group. The a priori required sample size (alpha = 0.05 and power = .80) to detect an effect similar to that found in Experiment 1 was 22, 11 participants per condition.

Participants, recruitment and randomisation procedure

Participants were recruited via two military veteran welfare support groups. The researcher attended group meetings to introduce the study and distribute a letter of invitation to participate that included study contact details. Inclusion criteria were to be a military veteran with a formal diagnosis of PTSD by a National Health Service or Ministry of Defence psychiatrist. Participants currently in receipt of psychological therapy were excluded. A total of 57 veterans contacted the study team and were assessed for eligibility by telephone. Of these, 9 did not meet inclusion criteria, and 23 declined to participate after receiving further information (15 did not like the idea of fishing, 6 were unavailable on study dates and 2 had childcare commitments), leaving a total sample size of 25. The 25 participants were randomly allocated using block randomisation to either the angling intervention group (n = 13) or waitlist control group (n = 12). Seven people subsequently did not turn up to the intervention. Recruitment began in July 2015 and data collection continued until December 2015 (4-month follow-up).

The intervention involved an angling experience exactly as described in experiment one. In addition to the angling coaches and a mental health practitioner, 3 military veteran participants from experiment one also attended in the role of ‘mentor’.

Repeated measures were taken for both groups 2 weeks prior to and 2 weeks following the intervention for the angling group. The waitlist participants were also reassessed two weeks after they subsequently completed the intervention and both groups were followed up 4 months after their own intervention (Fig 3). PTSD symptoms were assessed by the PCL-5 [59]. The PCL-5 is a twenty item self-report measure that assesses the twenty DSM-5 [1] symptoms of PTSD. The PCL-5 is reported to have sound psychometric properties with good internal consistency (.95), test–retest reliability (r .84), and convergent validity with the PCL-S (r .87) [60]. The range for the PCL-5 is 0–80; a cut-off score of 31–33 is suggestive of PTSD. Depression, anxiety and stress were assessed as in the first experiment. Two additional measures were included in experiment two. The Work and Social Adjustment scale [WSAS; 61] is a 5-item measure of impairment in general social functioning and has high internal reliability and sensitivity to treatment effects [62]. The maximum score is 40, with higher scores indicating greater impairment. A final measure was included to assess positive change in psychological growth, as opposed to merely absence of symptoms. The Psychological Wellbeing Post-Traumatic Changes Questionnaire [PWB-PTCQ; 63] has high internal consistency and sensitivity to change. Higher scores indicate more positive, post-traumatic change. The maximum score is 90, with scores over 54 indicating the presence of positive change. The measures were taken by an experimenter blind to experimental condition.

Fig 3

Summary of measurement and intervention timepoints for intervention and waitlist control group.

Randomisation checks

Characteristics of participants in the intervention and control groups are shown in the right-hand portion of Table 1. The two groups did not differ in age (p = .696), age when joined forces (p = .625), years served (p = .581) or years since discharge (p = .517). All but one of the participants were men, and equal numbers in each condition were unemployed and taking psychotropic medication. A between groups MANOVA showed that the two groups did not differ at baseline across psychological measures (F (6, 11) = 1.319, p = .326). The Univariate F values for the comparison of psychological measures at baseline are displayed in Table 4. These analyses confirm that randomisation was successful in distributing key individual differences evenly between groups.

Table 4

Summary of measures at baseline (2 weeks prior) and 4 weeks (2 weeks post-intervention) by intervention and waitlist control groups and effect size of mean difference between intervention and control groups at 4 weeks.

		Intervention Group	Waitlist Control Group	Between Groups Univariate F value df (1,16)	Cohen’s d [95% CI]
		(n = 9)	(n = 9)
Measure	Timepoint	Mean (SD)	Mean (SD)	F (p)
PCL (PTSD)	Baseline	47.00(15.98)	55.67(12.35)	1.657 (.216)	-1.197 [-2.2, -0.194]
	4 weeks	33.78(18.45)	53.67(14.56)	6.503 (.021)
PHQ (Depression)	Baseline	18.00(6.16)	19.00(4.80)	.148 (.706)	-1.66 [-2.732, -0.589]
	4 weeks	10.44(6.20)	19.22(4.18)	12.389 (<0.001)
GAD (Anxiety)	Baseline	13.44 (4.00)	15.89(3.79)	1.770 (.202)	-1.623 [-2.688, -0.558]
	4 weeks	8.22(4.76)	15.78 (4.55)	11.841 (.003)
PSS (Stress)	Baseline	24.11(7.17)	27.56 (4.75)	1.445 (.247)	-1.988 [-2.956, -0.747]
	4 weeks	17.56 (5.81)	29.11(6.64)	15.429 (.001)
WSAS (Work and social adjustment)	Baseline	21.89 (7.04)	23.22(10.89)	.095 (.762)	-0.787 [-1.746–0.172]
	4 weeks	15.44 (8.35)	22.556 (9.671)	2.787 (.114)
PWB-PTCQ Posttraumatic wellbeing	Baseline	47.56(11.09)	49.50(16.33)	.082 (.778)	1.279 [0.265–2.293]
	4 weeks	65.78(8.98)	48.89(16.37)	7.360 (.015)

Comparison of control and intervention groups

The key analysis relates to the comparison of pre- (week 0) and post-intervention measures for the intervention and control groups taken at week 4 (see Fig 3). A mixed MANOVA with one between-groups factor (intervention vs. waitlist control) and repeated measures on all outcomes (baseline vs. 2 weeks post intervention) revealed a non-significant main effect of group (F (6, 11) = 2.061, p = .141, partial eta2 = .529), a significant main effect of time (F (6,11) = 3.626, p = .031, partial eta2 = .664) that was qualified by the important interaction of group by time (F (6,11) = 3.547, p = .033, partial eta2 = .659). Inspection of the univariate F values showed that all variables contributed to this interaction effect (F (1,16) = 8.445, p = .01, partial eta2 = .345 (PTSD symptoms), 19.982, p < .001, partial eta2 = .555 (depression), 11.225, p = .004, partial eta2 = .412 (anxiety), 13.474, p = .002, partial eta2 = .457 (work and social adjustment), 4.610, p = .047, partial eta2 = .224 (stress), 12.148, p = .003, partial eta2 = .432 (post-traumatic growth)). A summary of the means, standard deviations and univariate between groups F tests at time two are summarised in Table 4. At two weeks post-intervention, participants in the intervention group had significantly lower PTSD symptomology, depression, anxiety, and perceived stress relative to controls, and also reported post-traumatic growth relative to controls.

Change in wellbeing across time

Since all participants eventually completed the angling activity experience it was also possible to examine change across time for all 18 participants combined. These analyses provide a replication and extension of findings from experiment one. A MANOVA with repeated measures was conducted across all measures at 3 timepoints (2 weeks prior to intervention, 2 weeks post and 4 months post; see Fig 3 for respective weeks of measurement). Results revealed a significant multivariate within-participants effect (F (12, 6) = 7.492, p = .011, partial eta2 = .937). Inspection of univariate within participant effects showed that change in psychological measures across 3 time points was significant for all measures (F (2,34) = 26.254, p < 0.0001, partial eta2 = .607 (PTSD symptoms), 43.799, p < 0.0001, partial eta2 = .720 (depression), 25.730, p < 0.0001, partial eta2 = .602 (anxiety), 16.123, p < 0.0001, partial eta2 = .487 (perceived stress), 13.493, p < 0.0001, partial eta2 = .442 (work and social adjustment), 15.404, p < 0.0001, partial eta2 = .475 (posttraumatic growth)). A summary of means, standard deviations, pairwise t-tests comparing pre-intervention with 2-week and 4-month follow-up respectively is displayed in Table 5. Results show that participants experienced a decline in PTSD symptoms, depression, anxiety and stress, with improved work and social functioning and increased post-traumatic growth. Cohen’s d effect sizes were calculated according to Lenhard & Lenhard [56]. As in experiment one, effect sizes were large and sustained to 4 months.

Table 5

Summary of measures at two weeks pre-intervention, two weeks post-intervention and 4 months post-intervention for combined sample (Experiment 2: N = 18): Pairwise t value, Cohen’s d and 95% confidence interval.

Measure	Timepoint	Mean (SD)	Pairwise t value, df = 17 (p-value) comparison with baseline pre intervention	Cohen’s d [95% CI] For comparison with baseline pre-intervention
PTSD symptoms (PCL-5)	Pre-intervention	50.33 (15.15)
	2 weeks post	34.56 (15.52)	5.399 (< .001)	-1.287 [-2.01, -0.57]
	4 months post	37.06 (15.41)	5.346 (< .001)	-1.27 [-1.99, -0.55]
Depression (PHQ-9)	Pre-intervention	18.61 (5.150)
	2 weeks post	10.89 (5.54)	7.830 (< .001)	-1.922 [-2.71, -1.13]
	4 months post	12.50 (5.04)	6.113 (< .001)	-1.43 [-2.16, -0.7]
Anxiety (GAD-7)	Pre-intervention	14.61 (4.33)
	2 weeks post	9.06 (4.70)	5.644 (< .001)	-1.389 [-2.12, -0.66]
	4 months post	10.17 (3.99)	4.710 (< .001)	-1.068 [-1.77, -0.37]
Stress (PSS)	Pre-intervention	26.61 (7.18)
	2 weeks post	18.94 (5.82)	4.302 (< .001)	-0.928 [-1.62, -0.24]
	4 months post	19.78 (5.91)	3.779 (< .001)	-0.819 [-1.50, -0.14]
Work and social adjustment (WSAS)	Pre-intervention	22.22 (8.21)
	2 weeks post	15.33 (9.16)	4.040 (< .001)	-1.015 [-1.71, -0.32]
	4 months post	16.89 (8.65)	3.319 (< .004)	-.804 [-1.48, -0.13]
Post traumatic growth (PWB-PTCQ)	Pre-intervention	48.22 (13.58)
	2 weeks post	63.78 (11.01)	-5.549 (< .001)	1.206 [0.5, -1.92]
	4 months post	62.11 (14.35)	-4.326 (< .001)	1.051 [0.35–1.75]

As in experiment one, further analyses were conducted to evaluate clinical significance of findings both between the baseline and 2-week post intervention and the baseline and 4-month follow-up time points. As previously, analyses were conducted for the PCL-5 symptoms first including all participants and then including only those who scored above the clinical cut-off—score of 33 as recommended in Wortmann et al., [60] at pre-intervention baseline. In computing the Reliable Change Index, the Cronbach’s alpha used within this calculation was 0.95, derived from Wortmann et al., [60].

For the whole sample pre-post intervention, 12 (67%) made reliable improvement; 6 (33%) did not reliably change and no-one deteriorated in their PTSD symptoms. In relation to CSC, 5 (28%) made clinically significant change in their PTSD symptom scores. When those who scored below the clinical cut-off at baseline were excluded (n = 3), 5 made clinically significant change in their PTSD symptom scores. Fig 4 illustrates the reliable and clinically significant changes pre-post intervention for the 18 participants.

Fig 4

Reliable and clinically significant change in PTSD symptoms (using external criterion for PCL-5) at two weeks’ follow-up, Experiment two.

(N = 18).

For the whole sample baseline-4 month follow-up, the same pattern of results were found, 12 (67%) made reliable improvement; 6 (33%) did not reliably change and no participant reported deterioration in their PTSD symptoms. In relation to CSC, 5 (28%) made clinically significant change in their PTSD symptom scores. When those who scored below the clinical cut-off at baseline were excluded (n = 3), 5 made clinically significant change in their PTSD symptom scores.

General discussion

Research on the therapeutic potential of outdoor recreational experiences for military veterans with PTSD is in its infancy. The goal of the present studies was to provide formal evaluation of the potential impact of brief outdoor activity experiences amongst military veterans with diagnosed PTSD who were not receiving any form of psychological therapy. The results of the two experiments, comprising locally delivered, outdoor recreational interventions amongst veteran peers, demonstrate not only the potential of motivating veterans with PTSD to engage with such an approach but also its potential clinical usefulness. In both studies and in line with our hypotheses, veterans showed a clear and sustained improvement in symptomology relating to PTSD, depression, anxiety and stress as a consequence of the experience. In addition, in the second experiment, measures of post-traumatic growth alongside work and social adjustment were both found to improve following the intervention. Experiment two also provided important evidence that participants randomly allocated to the therapeutic recreation experience experienced symptomatic change that differed significantly from those randomised to a waitlist control group.

These findings not only add to the previous literature in terms of the potential usefulness of outdoor recreational interventions in the treatment of PTSD and its comorbidities but also extend and strengthen the evidence in three essential ways: Firstly, only participants who were not currently in receipt of psychotherapy were enrolled onto the studies; this is important as some previous studies have included participants in receipt of therapy, making it difficult to distinguish benefit derived from the intervention from that derived from ongoing psychotherapy; Secondly, the interventions employed in the present studies were all relatively brief, conducted close to participants’ homes and at low cost, demonstrating not only the potential but also the relative ease and affordability of such an approach; Thirdly, the second experiment employed a control (waitlist) condition, thereby facilitating a more robust interpretation of the findings—something that has only been done twice previously in the literature of this field [35].

Another aspect of the experiments reported here is that all participants in both studies had a National Health Service or Military Physician diagnosis of PTSD. They were followed up to 4 months and data subjected to additional analyses of reliable and clinically significant change. Previous studies of an outdoor experience directed at military veterans have not considered reliable or clinically significant change, relying upon statistical significance that assesses mean difference without reference to the relevance of the effect [35]. For example, statistical significance may be obtained if a participant score changes within a non-clinical range. Analyses from both studies showed that a substantial proportion of participants showed reliable improvement in PTSD symptoms 4 months following the intervention, figures that are in line with those reported for psychotherapy [e.g. 21].

A variety of different experiences were explored in the present studies. They all incorporated common elements of our procedure, namely exclusive use of outdoor facilities by veterans with diagnosed PTSD, safety briefing, allocation to professional recreation trainers in a ratio of 2:1, communal food preparation and socialising by participating veterans. No formal psychological therapy was offered or provided to participants during the experience. Findings of the experiment one multivariate analysis showed that within participants’ change in wellbeing across time was not qualified by type of activity pursued. This is the first study to compare different outdoor experiences and findings suggest that the type of outdoor activity experienced was not necessarily a critical factor in the results obtained. Active intervention elements appear to be those held in common, namely professional instruction in an outdoor recreational activity in the company of peers [c.f. 36]. Additionally, evidence suggests that readily available local environments such as a stocked fishing lake can deliver benefits similar to those previously obtained in more wild and exotic locations [35].

Strengths and limitations

The present studies have many strengths. They studied military veterans with diagnoses of PTSD from a national health service or military psychiatrist, and employed a formal procedure for the outdoor activity experience. Measures were taken at baseline and participants were followed for four months. No participant was lost to follow-up. Most important, experiment two employed a waitlist control group and random allocation to condition.

Nonetheless, a number of limitations should be acknowledged. Due to ethical considerations, the comparison of the waitlist control and experimental groups was restricted to two weeks and it would be desirable to replicate this effect over a longer time period. Although waitlist participants received the same phone calls and administration of measures, future studies might also employ an active rather than passive waitlist control condition. This is important as it would help to address any possible issues of participants’ expectations from the experience and respondent bias (e.g. acquiescence and social desirability bias). It should be acknowledged that the majority of participants were men and generalisation to women veterans with PTSD is therefore uncertain. The intervention format, together with the hard to reach population necessitates the involvement of small groups of veterans, as previously noted by Bird [31]. Nonetheless the current evidence presented shows that these small sample sizes were sufficiently powered to detect the effect sizes observed. A total of 48 veterans with untreated PTSD, mostly with chronic PTSD, took part in these studies and evidence showed that more than half of the participants experienced change in PTSD symptoms that is indicative of reliable change of clinical significance. Some participants in these studies have subsequently made social and economic gains by entering education, employment, deciding to engage in psychotherapy, and regaining access to children. Some have trained as fishing coaches. All now have access to a support group of veterans with PTSD with shared experience of learning to adapt to civilian life.

Conclusions

Accumulating evidence across nations provides support for the role of therapeutic outdoor recreation in addressing the particular psychological needs of military veterans with PTSD. The use of outdoor recreational activities to ameliorate PTSD and co-morbid symptoms and improve well-being in military veterans appears to be a viable and useful treatment option. Further research is indicated to evaluate and promote the availability of this and other programs to the millions of men and women adapting to life after war. This is particularly important for a clinical population who are traditionally thought to be difficult to engage in formal therapies and yet whose continued ill health is a considerable burden to the individuals, families and communities involved.

Protocol—Pilot study.

(DOCX)

Click here for additional data file.

Protocol—RCT.

(DOCX)

Click here for additional data file.

CONSORT 2010 checklist of information to include when reporting a randomised trial*.

(DOC)

Click here for additional data file.

18 May 2020

PONE-D-19-35181

Outdoor recreational activity experiences improve psychological wellbeing of military veterans with post-traumatic stress disorder: positive findings from a pilot study and a randomised controlled trial

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Reviewer #1: The two related studies reported in the manuscript investigate the short- and mid-term psychological effects of very brief (1-day) recreational interventions for participants with PTSD. Although considerable favourable changes in several meaures are reported, these results are, in my opinion, of doubtful value by themselves fort he following reasons. Firstly, the outcome measures are subjective, self-reported ones obtained in participants who were not blinded tot he intervention. Thus, positive effects may well occur due to participants‘ expectations or to general beneficial effects due to receiving attention. The comparison with the waiting list in experiment two unfortunately does not deal effectively with this deficit. Secondly, although this is entirely a layman’s opinion, I cannot imagine that a single day’s activity could yield a meaningful, enduring benefit in people who have been suffering PTSD for many years.

Further important weaknesses:

(1) the calculation oft he reliable change index (RCI) is incompletely described. The calculation of ‚standard error‘ must incorporate a reliability measure such as Cronbach’s alpha in ordert o arrive at a measure of measurement error rather than variability.

(2) The exclusion of cases with non-dysfunctional values at baseline in Figs. 2 and 4 induces an element of ‚regression tot he mean‘ in the subsequent changes and is thus biased in the direction of favourable changes.

Minor points (by line number)

38-39 Ambiguity in AND and OR

233 Please state the randomisation method

Tab. 1 years military service and years since leaving are mean (SD)?

244 Please state explicitly: only one session on one day

294-5 What is meant by ‚first‘ and ‚subsequent‘ interventions?

305 Main effect of intervention group is not interpretable, since all groups were equally treated at baseline

316 Describe or cite method for effect sizes, rather than just citing the web-site

346 ‚Clinical range‘ means dysfunctional range?

372 Why was angling chosen for experiment 2?

377-8 Which ethical considerations preclude a 4-month wait (they have already ‚waited‘ so many years!)?

388 ‚Effect‘ means between-groups at post-intervention timepoint?

409 Make clear that ‚intervention‘ refers to intervention period of the intervention group, not the subsequent intervention after waiting

Tab. 3 Why refer to ‚4 weeks‘ – better as in Table 2 ‚2 weeks prior‘ and ‚2 weeks post‘

521 There were 3, not 4, interventions?

536 Why would including participants with psychotherapy bias the results?

573 Active control group is important in order to reduce ‚expectation‘ or ‚attention‘ bias

Reviewer #2: Dear Editor,

Thank you for inviting me to review this manuscript. I believe that the topic is very interesting and that the authors put effort in drafting this work. The aim of this study was to enhance the knowledge regarding brief outdoor activity experiences amongst military veterans with diagnosed PTSD. After reading the manuscript, I was also left with a few questions about the work and I believe addressing these will enhance the contribution to the literature. Questions/concerns are outlined by manuscript section below.

Introduction

It is not clear what are each study objectives and hypothesis

1. Study objectives: Abstract [line36]: “Two studies were conducted to evaluate this possibility”. The authors should clearly state what where the specific objectives for each study in the introduction, and in the abstract.

2. Study hypothesis [line 201-5]: “It was hypothesized that participants would experience a reduction in symptomology as a consequence of the experience.” …“The hypothesis that experimental participants would experience benefit relative to controls was supported.”

• The study hypothesis are vague and not clear. For example what do the authors refer in “symptomology “or “benefit”?

• To improve it would recommended stating for each study hypotheses what are the outcome measures and detraction of association.

Methods:

I recommend strengthening and clarifying the methods section, as detailed below.

1. Experiment One Design [line 219]: Could the authors please clarify, based on my understanding all 3 group received intervention, there is no control group as such, this design isn’t RCT.

2. Random allocation: There could be much more clarity in the Methods about who and what methods where used to generate random allocation to interventions groups.

3. Participants: “Eligibility criteria: military veteran with a formal diagnosis of PTSD by a National Health Service or Ministry of Defence psychiatrist. None were currently receiving psychological therapy for PTSD.”

• It isn’t clear what methods and process where used to verify formal diagnosis of PTSD [medical recorders, was it based on self –report?]

• Given that ‘military veteran’ differs between countries and governments, could the authors please clearly how they define ‘veteran’ in the study?

• There could be much more clarity in the Methods regarding the screen process/data collection, the authors present in Table 1. The summary of participant characteristics [include years’ military service, years since leaving service etc. ]. However, it is not clear how the data was collect. This should have been clearly signposted in the Methods.

4. Intervention descriptions: There could be much more clarity in the Methods about interventions, seating it accrued in each study. Perhaps with the addition of a table which illustrates each intervention group in in each study?

• What was the duration to each session in each intervention group (angling, horse husbandry and riding, falconry and archery)

• What was the activities in each intervention groups? what tools been used how long ? etc..

• How many professional coaches in each intervention group

• What was the training, that professional coaches who provide the intervention had to undertake?

Etc…

5. Measurements:

• In the aims [line 193] the authors stated: We designed two experiments to contribute to and extend previous literature by providing an evaluation of the feasibility and effects of brief peer group outdoor recreational”. Could the authors please clarify, how feasibility of the intervention was assessed – please describe how it was done and be how?

• To help the reder interpret the effect size, please provide the score range for each of the outcome measure that been used in the study.

6. Statistical Analyses: Some additional detail and clarification of the data analysis steps used would be helpful. Given the small sample could the authors please add additional information which analysis were used to evaluated inferential analyses and relevant statistical assumptions (including normality, linearity, homoscedasticity).

7. The following statement are not fully supported by the results of this study: “The results of the two experiments, comprising four local, outdoor recreational interventions, demonstrate not only the feasibility of motivating veterans with PTSD to engage with such an approach but also its potential clinical usefulness”.

8. I am concerned that the authors may be over-interpreting the results of the study. The authors stated in the general discussion: “Another aspect of the experiments reported here is that all participants in both studies had an NHS or Military Physician diagnosis of PTSD. They were followed up to 4 months and data subjected to additional analyses of reliable and clinically significant change. Previous studies of an outdoor experience directed at military veterans have not considered reliable or clinically significant change, relying upon statistical significance that assesses mean difference without reference to the relevance of the effect”.

However:

• It is not clear what was the diagnosis or the severity of PTSD. Potently it could be that the Veteran that agreed to participants were diagnosed with PTSD who is less severe.

• Furthermore, in the analysis it is not clear way the authors used Jacobson and Truax [not in veteran population] nor way they decided to remove segments from the tool. Which led to reduction in the sample to 18.

The PCL-M is among few validated measures of PTSD severity both in line with the DSM-5 and demonstrating excellent psychometric properties. Preliminary cut-scores of both 33 and 38 have been recommended as indicating PTSD presence. These validation efforts were implemented among veteran samples, and optimal PCL cut-scores vary across populations depending on factors like trauma type. It would recommended to use the full valid tool PCL-5 and updated research. Please see: Kazdin AE. Methodological issues and strategies in clinical research. 3rd ed.

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Reviewer #1: Yes: Jeremy Franklin

Reviewer #2: No

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12 Jun 2020

Response to Reviewers

We would like to begin by thanking our editor and both of our reviewers for their careful reading of our paper and for their constructive comments and suggestions. For ease of reading, we have formatted our responses in blue text.

Editor:

The reviewers have raised a number of concerns that need attention. They request additional information on methodological aspects of the study and the analyses, and they have raised some concerns about the conclusions and their interpretation.

We are grateful to the reviewers for noting aspects of our manuscript that required further elaboration or clarification in order to enhance the contribution of the work to the literature. We have outlined our response to each of the points raised by your reviewers in the following sections. In particular we have added information to clarify details of our methods and analysis. We have also reflected upon our interpretation and discussion and conclusion sections to ensure that the claims are not overstated. We consider that these revisions have resulted in an improved manuscript and look forward to receiving your response. We have also checked the layout and style requirements for publication.

Reviewer #1: The two related studies reported in the manuscript investigate the short- and mid-term psychological effects of very brief (1-day) recreational interventions for participants with PTSD.

Although considerable favourable changes in several measures are reported, these results are, in my opinion, of doubtful value by themselves for the following reasons.

• Firstly, the outcome measures are subjective, self-reported ones obtained in participants who were not blinded to the intervention. Thus, positive effects may well occur due to participants‘ expectations or to general beneficial effects due to receiving attention. The comparison with the waiting list in experiment two unfortunately does not deal effectively with this deficit.

o Thank you for taking the time to review our paper and for your evaluation of the paper as technically sound, and that the data support the conclusions. As discussed in the introduction (lines 176-216) and noted by reviewer 2 the studies extend existing literature concerning outdoor activity interventions for military veterans. The current studies build upon prior research in several ways, for example by employing power analyses, a control group and longer follow up. The measures we used are well respected, validated and established measures of PTSD, depression, anxiety etc. commonly employed to assess psychotherapy outcomes. (Please also see response to Reviewer 2’s 1st comment below). Nonetheless, we do not assert yet that this is a definitive trial of this approach and in the discussion sections acknowledge the limitations of a waitlist control group, for example, and call for further research, that is indicated by this contribution to the literature. Also, we have added to the discussion (please see response to your final comment below and lines 627-631 with respect to the potential issue of bias and expectancy.

• Secondly, although this is entirely a layman’s opinion, I cannot imagine that a single day’s activity could yield a meaningful, enduring benefit in people who have been suffering PTSD for many years.

o These interventions perhaps need to be viewed in the context of a population who employ avoidant coping responses and have done so for many years. Some participants rarely left their homes. This is explained in the introduction (pages 4-8). The intervention has three important elements: being amongst other veterans with PTSD (peers), learning a new activity and being outdoors (lines 136-165). We agree that the results may surprise people but would point out that these single days comprise many hours (equating to many sessions of psychotherapy if looked at another way), and to our use of established measures of trauma, mental health and wellbeing. Our findings progress the literature in this field and provide new, improved evidence that paves the way for more sophisticated research designs and research funding that may address the limitations you pose. We have fully acknowledged these limitations in the discussion section of the paper.

o Perhaps also very important, organisations around the world are offering interventions of this kind to this client group (and in some cases at a fee) and our research contributes to development of an evidence assessment for this work, including assessment that it does no harm and development of more detailed protocols.

Further important weaknesses:

(1) the calculation of the reliable change index (RCI) is incompletely described. The calculation of‚ standard error‘ must incorporate a reliability measure such as Cronbach’s alpha in order to arrive at a measure of measurement error rather than variability.

We have now addressed this issue by adding:

1) “The Cronbach’s alpha used within this calculation was 0.94, which was taken from Sutker, Davis, Uddo and Ditta (57)” to lines 370-1 and

2) “In computing the Reliable Change Index, the Cronbach’s alpha used within this calculation was 0.95, derived from Wortmann et al., (60).” To lines 542-3

(2) The exclusion of cases with non-dysfunctional values at baseline in Figs. 2 and 4 induces an element of ‚regression to the mean‘ in the subsequent changes and is thus biased in the direction of favourable changes.

The Figures 2 and 4 did show the data only for those participants with dysfunctional values at baseline. Since both reviewers prefer a different approach we have now presented new figures 2 and 4 that show data from the entire samples in experiments one and two. These revised figures with full samples now permit the reviewer and reader to view the change in scores of every participant and consider for themselves the changes. We agree that exclusion of those who (conventionally) would not be considered dysfunctional at baseline may cause regression to the mean. On the other hand, not excluding these participants means that calculation of clinically significant change might inadvertently refer to a change within the non clinical (non dysfunctional) range- for example a person might obtain a significantly reduced PTSD symptom score but this change could be within the range of non-dysfunctional values. This issue is debated in the literature. We therefore chose to present the calculations of CSC with and without exclusions and reported this in full in our manuscript for transparency. Edits have been made to the text and figure captions on lines 378-9 & 391-2 (experiment 1) and lines 548-552 (experiment 2) to ensure this is clear.

Minor points (by line number) – please note – line numbers have now changed from the original; we have referred to the new line numbers in blue text.

38-39 Ambiguity in AND and OR

Corrected, line 41 – “angling, equine care, or archery and falconry combined”

233 Please state the randomisation method

The manuscript has been updated to include this information: “Participants were randomly allocated (using an online randomisation tool – www.random.org) to either an angling, equine husbandry or falconry and archery recreational experience.” (now lines 251-2).

Tab. 1 years military service and years since leaving are mean (SD)?

Corrected – (SD) added in table. Line 2.

244 Please state explicitly: only one session on one day

Yes that is correct. We have now clarified - “Each intervention was designed to deliver a day-long outdoor recreational experience”. Now line 265.

294-5 What is meant by ‚first‘ and ‚subsequent‘ interventions?

As noted on line 236 the three interventions with independent samples (angling, equine and falconry and archery combined) took place sequentially. This was simply relating to the fact that after the first intervention session that we ran, a Facebook page was set up. At subsequent sessions (with different participants), we made the participants aware of the Facebook page. We have re-written line 329 so that it now states: “at the end of the first of the three sequentially run interventions…”.

305 Main effect of intervention group is not interpretable, since all groups were equally treated at baseline

Here, a main effect of group refers to a difference between the different types of intervention (angling v equine v falconry) – there was no effect of group, indicating that all interventions had a somewhat similar effect. Now line 343-6.

316 Describe or cite method for effect sizes, rather than just citing the web-site

Now line 354. The reference to Lenhard & Lenhard (2016) has been added.

346 ‚Clinical range‘ means dysfunctional range?

We have added “not scoring in the dysfunctional range for PTSD diagnosis” to clarify. Now lines 384-5.

372 Why was angling chosen for experiment 2?

We have added the following for clarification: “Angling was chosen as it is an appealing pastime for our target participants and is a readily accessible and relatively inexpensive hobby to pursue should participants wish to continue after their intervention.” Now lines 408-10. Results of experiment one showed that the 3 activities we explored produced very similar results.

377-8 Which ethical considerations preclude a 4-month wait (they have already ‚waited‘ so many years!)?

Now line 416.

There were 2 main reasons. (Perhaps they could be considered both practical and ethical). (1) We were keen to retain participants allocated to the waitlist control group to the experiment and (2) the charity that assisted us in recruitment also felt it unethical to offer and then enforce a 4 month wait. We are happy to change this to “Practical considerations” if you prefer.

388 Effect‘ means between-groups at post-intervention timepoint?

The power calculation was based on the repeated measures effect (2 weeks pre v 2 weeks post) for the angling intervention group. Now lines 421-2.

409 Make clear that ‚intervention‘ refers to intervention period of the intervention group, not the subsequent intervention after waiting

Done. Now lines 449.

Tab. 3 Why refer to ‚4 weeks‘ – better as in Table 2 ‚2 weeks prior‘ and ‚2 weeks post‘

Simply due to space in the table. We have added some clarity in the table legend to help make the comparison with table 2 easier. Lines 505-6. NB Table 3 is now Table 4 and Table 2 is Table 3.

521 There were 3, not 4, interventions?

We were referring to the 3 interventions in the first experiment and the 1 in the second. As this may cause some confusion, we have now removed reference to the number of interventions. Now line 569.

536 Why would including participants with psychotherapy bias the results?

This is a very pertinent question, is something that possibly obscures the findings of previous studies done in this area and was one of the driving factors for us undertaking these two studies. We introduce our rationale in the introduction in lines 188-94: “First, we excluded all potential participants who were in receipt of psychotherapy. Military veterans often avoid psychotherapeutic treatment for many years, and as noted by Gelpkof (32), interventions such as these may be particularly valuable for those not yet ready to engage, who have not benefitted or who have been treatment drop outs. Also, the inclusion of participants who were concurrently receiving psychotherapy in some previous studies (e.g. 40) makes it difficult to discern if benefit arose from the intervention or from ongoing treatment”. We see this as one of the strengths of our study and also refer to it again in the discussion – lines 582-6.

573 Active control group is important in order to reduce ‚expectation‘ or ‚attention‘ bias

This is a fair point and one that is related to your 1st point (above). We have added “This is important as it would help to address any possible issues of participants’ expectations from the experience and respondent bias (e.g. acquiescence and social desirability bias)” to lines 628-30.

Reviewer #2:

Thank you for inviting me to review this manuscript. I believe that the topic is very interesting and that the authors put effort in drafting this work. The aim of this study was to enhance the knowledge regarding brief outdoor activity experiences amongst military veterans with diagnosed PTSD. After reading the manuscript, I was also left with a few questions about the work and I believe addressing these will enhance the contribution to the literature. Questions/concerns are outlined by manuscript section below.

Thank you for your positive reaction to the manuscript and very useful suggestions to enhance the contribution. We outline our responses below.

It is not clear what are each study objectives and hypothesis

1. Study objectives: Abstract [line36]: “Two studies were conducted to evaluate this possibility”. The authors should clearly state what where the specific objectives for each study in the introduction, and in the abstract.

Thank you for helping us to make this more explicit. We have now added in a more specific aim in lines 35-39: ‘In particular, these studies aimed to test the hypothesis that a brief group outdoor activity would decrease participants’ symptoms as assessed by established measures of PTSD, depression, anxiety and perceived stress, and increase participants’ sense of general social functioning and psychological growth.’

2. Study hypothesis [line 201-5]: “It was hypothesized that participants would experience a reduction in symptomology as a consequence of the experience.” …“The hypothesis that experimental participants would experience benefit relative to controls was supported.”

• The study hypothesis are vague and not clear. For example what do the authors refer in “symptomology “or “benefit”?

• To improve it would recommended stating for each study hypotheses what are the outcome measures and detraction of association.

Again, thank you for helping us to make this more explicit. We have now added: ‘It was hypothesized that participants would experience a decrease in symptoms as assessed by established measures of PTSD, depression, anxiety and perceived stress as a consequence of the experience’ on lines 209-11 and ‘The hypotheses that experimental participants would experience a decrease in symptoms of PTSD, depression, anxiety and perceived stress and an improvement in ratings of general social functioning and psychological growth, relative to controls, were supported.’ On lines 213-16.

Methods:

I recommend strengthening and clarifying the methods section, as detailed below.

1. Experiment One Design [line 219]: Could the authors please clarify, based on my understanding all 3 group received intervention, there is no control group as such, this design isn’t RCT.

Now lines 233. Yes, you are correct. In study one, all 3 groups received an outdoor recreational intervention (no control group, not an RCT) and all participants took part in only one of the interventions. The between groups factor here relates to the three different intervention experiences (angling vs. equine vs falconry and archery combined).

2. Random allocation: There could be much more clarity in the Methods about who and what methods where used to generate random allocation to interventions groups.

The manuscript has been updated to include this information: “Participants were randomly allocated (using an online randomisation tool – www.random.org) to either an angling, equine husbandry or falconry and archery combined recreational experience.” (now lines 251-2). Other points of clarification have also been addressed (please see below).

3. Participants: “Eligibility criteria: military veteran with a formal diagnosis of PTSD by a National Health Service or Ministry of Defence psychiatrist. None were currently receiving psychological therapy for PTSD.”

• It isn’t clear what methods and process where used to verify formal diagnosis of PTSD [medical recorders, was it based on self –report?]

We have now added the following to the manuscript: “Diagnosis was confirmed through documents showing a formal diagnosis by a psychiatrist presented by the participants to Veterans First.” (now lines 245-6). See also line 240 introducing Veterans First.

• Given that ‘military veteran’ differs between countries and governments, could the authors please clearly how they define ‘veteran’ in the study?

We have added the following to the manuscript “Definition of the term military veteran differs between countries. In the UK, the term ‘military veteran’ applies to anyone person “who has performed military service for at least one day and drawn a day’s pay” (45; pg.2); however, all our participants had served in the military for considerably longer (mean length of 11 years (SD 6.12). A summary of participant characteristics (including service length) is shown in the left-hand portion of Table 1.” (now lines 246-50).

• There could be much more clarity in the Methods regarding the screen process/data collection, the authors present in Table 1. The summary of participant characteristics [include years’ military service, years since leaving service etc. ]. However, it is not clear how the data was collect. This should have been clearly signposted in the Methods.

We have now added this information to lines 259-60: “All screening and data collection were carried out via telephone interview by a research assistant.”

4. Intervention descriptions: There could be much more clarity in the Methods about interventions, seating it accrued in each study. Perhaps with the addition of a table which illustrates each intervention group in in each study?

• What was the duration to each session in each intervention group (angling, horse husbandry and riding, falconry and archery)

• What was the activities in each intervention groups? what tools been used how long ? etc..

• How many professional coaches in each intervention group

• What was the training, that professional coaches who provide the intervention had to undertake?

Thank you for this suggestion. We have now included a new table two in the manuscript (and a sentence referring to it – line 270) covering all of these points. On line 265 we also now make clear that each intervention was a day-long experience.

5. Measurements:

• In the aims [line 193] the authors stated: We designed two experiments to contribute to and extend previous literature by providing an evaluation of the feasibility and effects of brief peer group outdoor recreational”. Could the authors please clarify, how feasibility of the intervention was assessed – please describe how it was done and be how?

Thank you for pointing this issue out. We were using the term ‘feasibility’ in its common usage and not in the clinical trials sense. Therefore, in order to avoid misunderstandings, we have removed this term throughout the manuscript and substituted where appropriate. E.g. the old line 193 has been replaced with “and the potential for military veterans to engage in such interventions” (now line 202). Please also see below.

• To help the reader interpret the effect size, please provide the score range for each of the outcome measure that been used in the study.

Thanks for suggesting this useful addition. We have now added these ranges etc in lines 309-21 and 455-65.

6. Statistical Analyses: Some additional detail and clarification of the data analysis steps used would be helpful. Given the small sample could the authors please add additional information which analysis were used to evaluated inferential analyses and relevant statistical assumptions (including normality, linearity, homoscedasticity).

Small samples of course present challenges in terms of normal distribution. As you will see in the manuscript, we tested for homoscedasticity and when the Mauchley test was significant we applied Greenhouse-Geisser corrections to the relevant F-values. We have amended our manuscript to make that fact more prominent. (lines 33-40 and as previously 347) . Importantly, we have been strict in adhering to the Type I Error Rate (.05) that we set for our analyses. Therefore, you will see that we have not done what some authors do and highlight effects which are “suggestive”, “trend-level” or “approaching significance” - and therefore all effects that we discuss are both large in our sample and statistically significant. This strict/conservative approach mitigates against the inherent difficulties of evaluating statistical assumptions in small samples because it avoids making claims unless the evidence is very clear. Such claims should therefore remain sound even if it has been difficult to evaluate some statistical assumptions. Note, however, that our figures 2 and 4 show the distribution of scores for the most important of our dependent variables, and there is no suggestion there that outliers are driving the effect.

7. The following statement are not fully supported by the results of this study: “The results of the two experiments, comprising four local, outdoor recreational interventions, demonstrate not only the feasibility of motivating veterans with PTSD to engage with such an approach but also its potential clinical usefulness”.

Please see our response to the question 5 above relating to feasibility. We have also replaced that term for ‘potential’ on lines 570 and 588.

8. I am concerned that the authors may be over-interpreting the results of the study. The authors stated in the general discussion: “Another aspect of the experiments reported here is that all participants in both studies had an NHS or Military Physician diagnosis of PTSD. They were followed up to 4 months and data subjected to additional analyses of reliable and clinically significant change. Previous studies of an outdoor experience directed at military veterans have not considered reliable or clinically significant change, relying upon statistical significance that assesses mean difference without reference to the relevance of the effect”.

However:

• It is not clear what was the diagnosis or the severity of PTSD. Potently it could be that the Veteran that agreed to participants were diagnosed with PTSD who is less severe.

This is of course important. The Figures 2 and 4 have now been revised to show the before and after scores on PTSD for every participant who took part in experiment one and experiment two. This enables the reader to examine the PTSD of all participants and to observe the changes obtained in these experiments. We consider that this, together with the open access data ensure transparency. Please see also our response to reviewer one point 2. We have also now added information regarding the diagnosis of PTSD (please see reviewer 2 (yourself) point 3 also.

• Furthermore, in the analysis it is not clear way the authors used Jacobson and Truax [not in veteran population] nor way they decided to remove segments from the tool. Which led to reduction in the sample to 18.

The PCL-M is among few validated measures of PTSD severity both in line with the DSM-5 and demonstrating excellent psychometric properties. Preliminary cut-scores of both 33 and 38 have been recommended as indicating PTSD presence. These validation efforts were implemented among veteran samples, and optimal PCL cut-scores vary across populations depending on factors like trauma type. It would recommended to use the full valid tool PCL-5 and updated research. Please see: Kazdin AE. Methodological issues and strategies in clinical research. 3rd ed.

The benefits of using the Jacobsen and Traux (1991) method over just relying on cut-off scores on the measures is that this method allows for the percentage of participants achieving a reliable change (as indicated by the Reliable Change Index) to be reported alongside those achieving Clinically Significant Change. This method was similarly used when exploring the psychometric properties of the PCL-5 (Wortmann et al., 2016). The cut-off score of 33 was used within the experiment 2 RCSC analysis as recommended by Wortmann et al. (2016).

Submitted filename: response to reviewers.docx

Click here for additional data file.

9 Oct 2020

PONE-D-19-35181R1

Outdoor recreational activity experiences improve psychological wellbeing of military veterans with post-traumatic stress disorder: positive findings from a pilot study and a randomised controlled trial

PLOS ONE

Dear Dr. Cooper,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Overall, your revisions were well received by the reviewers. However, just a couple issues remain. These are straightforward but important and should be addressed.

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Ethan Moitra

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PLOS ONE

Brown University

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: (No Response)

Reviewer #2: (No Response)

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The authors have replied in detail and pertinently to all the reviewer’s points. There are just a couple of my points needing attention:

1. Original line 305 (now 346) Main effect of intervention group: the intervention effect is the interaction group x time, since we are looking for differences between the changes over time among the groups (compare statement of hypotheses in lines 213-215). The main effect includes baseline differences which are not a measure of intervention effect. Thus it should be clearly stated that the effect of the intervention(s) is measured and tested using the group x time interaction.

2. Original line 316 Method for effect sizes. Lenhard and Lenhard is now cited, but the linked web-site provides several alternative definitions of effect size. I could not be sure which one was appropriate, and my attempts to verify this by calculating the effect sized did not yield values in agreement with those in Table 3. Which method was used?

My reservations about the plausibility and conclusiveness of these results remain, but the authors have acknowledged the limitations and future readers should judge for themselves.

Reviewer #2: The authors have provided a comprehensive reply to the questions raised and also presented a greatly improved manuscript. The manuscript is well written, has important clinical message, and should be of great interest to the readers.

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Reviewer #1: Yes: Jeremy Franklin

Reviewer #2: Yes: Neomi Vin-Raviv

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13 Oct 2020

Dear Professor Moitra,

We thank the reviewers for their review of the manuscript and note that they are both content that the manuscript is technically sound, that the data support the conclusions, that the statistical analysis is appropriate and rigorous, that the data is fully available and that the manuscript is written in clear unambiguous English.

We also thank you for the opportunity to clarify the two remaining issues raised by Reviewer One. We provide our response below. We believe we have satisfactorily resolved the issues raised by Reviewer One. We have also taken this opportunity to complete a final review and proof read of the manuscript, since we are aware that the journal does not copy edit accepted manuscripts.

Reviewer #2: The authors have provided a comprehensive reply to the questions raised and also presented a greatly improved manuscript. The manuscript is well written, has important clinical message, and should be of great interest to the readers.

Author Response: We thank Reviewer Two for her positive comments about the manuscript including her observation concerning the importance of the clinical message and likely interest to your wider readership.

Reviewer #1: The authors have replied in detail and pertinently to all the reviewer’s points. There are just a couple of my points needing attention:

1. Original line 305 (now 346) Main effect of intervention group: the intervention effect is the interaction group x time, since we are looking for differences between the changes over time among the groups (compare statement of hypotheses in lines 213-215). The main effect includes baseline differences which are not a measure of intervention effect. Thus it should be clearly stated that the effect of the intervention(s) is measured and tested using the group x time interaction.

Author Response:

We believe that the reviewer has misunderstood or misread the design of experiment one. We believe that the analyses are correctly reported and interpreted in the current manuscript. The intervention effect is tested differently in experiment one and experiment two. To explain:

The design of experiment one is reported in the abstract (line 39: “experiment one employed a repeated measures design…”) and can also be viewed in Figure One. The statement of hypotheses relevant to experiment one appear on lines 209-211 and state that: “It was hypothesized that participants would experience a decrease in symptoms as assessed by established measures of PTSD, depression, anxiety and perceived stress as a result of the experience.” The reviewer 1 refers to the hypotheses of experiment two on lines 213-215. Experiment two was indeed a controlled experiment and the corresponding hypothesis was that experimental participants would experience a decrease in symptoms relative to controls. We have now made clear that the waitlist-controlled experiment is experiment two in the Aims by adding the words ‘experiment two’ on line 212.

In fact, in the previous round of reviews, Reviewer 2 (Methods: point one) had also sought clarification that in experiment one, all groups received an outdoor recreational intervention, that is, there was no control group as such, not an RCT. We confirmed that this is the case and that the between groups factor refers to the 3 different types of outdoor activity (lines 235-236). Consequently, from the mixed MANOVA, the important experimental effect that tests our hypothesis is the within-participant effect observed across all activity types as stated on line 347-348. Neither the statistical test of the between groups factor nor the group X time effect in this experiment test our hypothesis. The group X time interaction in this experiment (experiment one) tests whether the changes across time varied according to type of activity (because there is no control group as such). In other words, whether it made any statistical difference if participants experienced angling, or equine or falconry). It turned out that it did not (line 349-351).

Since the issue here seems to be merely one of stating clearly which is the important test of the hypothesis (as stated on line 343) we have sought to make this even clearer in the text:

“Participants’ mean psychological wellbeing before the intervention and at 2 weeks and 4 months after for each activity type are summarised in table 3. In order to assess the hypothesised change in psychological wellbeing from before to after the experience, a mixed MANOVA with one between groups factor (intervention type: angling, equine, falconry) and one within-participant factor (3 time points: two weeks pre-intervention, 2 weeks’ post intervention and 4 months post-intervention) was conducted on all four measures of psychological wellbeing. It was hypothesised that the analysis would reveal a significant within-participant effect.”

In experiment two, the reviewer is quite correct that the important intervention effect is the interaction of group x time because this analysis tests whether the change across time differed for the intervention group compared to the control group (see lines 496-7).

Reviewer 1:

2. Original line 316 Method for effect sizes. Lenhard and Lenhard is now cited, but the linked web-site provides several alternative definitions of effect size. I could not be sure which one was appropriate, and my attempts to verify this by calculating the effect sized did not yield values in agreement with those in Table 3. Which method was used?

Author Response:

Thank you for pointing out that readers may be unclear where to find this information on the cited website. We have now clarified.

The effect sizes shown in Table 3 are for pre-post pairwise comparisons of data. As the reviewer notes there are different methods for different types of data provided on https://www.psychometrica.de/effektstaerke.html

The effect size calculation we used was the one labelled 4: Effect sizes when measurement is repeated within a group (pre-post). We have added detail to the reference no. 56 (lines 816-8) so that together with the available raw data, a reader can calculate the effect sizes should they wish.

56. Lenhard W, Lenhard A. Calculation of effect sizes: Dettelbach: Psychometrica; 2016 [Available from: https://www.psychometrica.de/effektstaerke.html Calculation of Effect Sizes 4. Effect sizes when measurement is repeated within a group (pre-post)]

Finally, we have also run all 4 figures through the PACE image correction software.

Kind regards, Nick Cooper (on behalf of the authors).

Submitted filename: response to reviewers letter.docx

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21 Oct 2020

Outdoor recreational activity experiences improve psychological wellbeing of military veterans with post-traumatic stress disorder: positive findings from a pilot study and a randomised controlled trial

PONE-D-19-35181R2

Dear Dr. Cooper,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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Kind regards,

Ethan Moitra

Academic Editor

PLOS ONE

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Reviewers' comments:

29 Oct 2020

PONE-D-19-35181R2

Outdoor recreational activity experiences improve psychological wellbeing of military veterans with post-traumatic stress disorder: positive findings from a pilot study and a randomised controlled trial

Dear Dr. Cooper:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

If we can help with anything else, please email us at plosone@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Ethan Moitra

Academic Editor

PLOS ONE