Validity and reliability of the German translation of the Diabetes Foot Self-Care Behavior Scale (DFSBS-D).

INTRODUCTION: Comprehensive regular foot self-care is one of the most critical self-management behaviors for people with diabetes to prevent foot ulcer development and related complications. Yet, adequate foot self-care is only practiced by very few of those affected. To improve diabetic foot syndrome prevention, a valid and reliable instrument for measuring daily foot-care routines in patients with diabetes is needed. However, no such instrument is currently available in the German language. This study, therefore, aims to translate and cross-culturally adapt the "Diabetic Foot Self-Care Behavior Scale" (DFSBS) into German (DFSBS-D) and evaluate its validity and reliability.
MATERIAL AND METHODS: The DFSBS was translated from English into German using a forward-backward procedure as per previous recommendations. Factor analysis was used to study structural validity. To establish construct validity, 21 a priori hypotheses were defined regarding the expected correlation between scores on the new German version (i.e., DFSBS-D) and those of the following questionnaires measuring related constructs: (1) German version "Diabetes Self-Care Activities Measure" (SDSCA-G), (2) "Frankfurter Catalogue of Foot Self-Care" (FCFSP), and (3) "Short Form 36" (SF-36) and tested in 82 patients. To assess test-retest reliability, patients completed the DFSBS-D again after a 2-week interval. Test-retest reliability was assessed from stable patients' data (n = 48) by calculating two-way random-effects absolute agreement ICCs with 95% CI and Bland and Altman analyses. In addition, Cronbach's alpha was calculated as internal consistency measure.
RESULTS: The 7-item DFSBS-D showed good structural validity. Its single factor explains 57% of the total sample variance. Of the 21 predefined hypotheses, 13 (62%) were confirmed. The DFSBS-D's internal consistency was good (Cronbach's alpha = 0.87). Test-retest reliability over a 2-week interval was also good (ICC 0.76).
CONCLUSION: The DFSBS was successfully translated into German. Statistical analyses showed good DFSBS-D structural validity, test-retest reliability, and internal consistency. Yet, construct validity may be debated.

Introduction

Diabetes mellitus (DM) prevalence has reached epidemic proportions and continues to rise–even in the younger population [1, 2]. Not only has DM a substantial impact on the lives of each affected individual, it also poses considerable socio-economic problems for the whole society [3-5]. Diabetes mellitus is characterized by long-lasting, high blood sugar levels, eventually damaging various organ systems, including the vascular and nervous systems [6]. Diabetic foot syndrome (DFS) is one of the most common DM sequelae [7, 8]. It encompasses various clinical pictures in the patient’s foot region and is associated with multiple serious complications [8]. Delayed or ineffective management can even result in amputation of the entire lower limb. In Germany, DM-related amputations are performed every 15 minutes, where up to 70% of patients die within five years following the surgery [9].

To avoid DM-associated foot complications, timely identification of individuals at risk for developing foot problems is of utmost importance [8]. In this context, regular adequate foot self-care is one of the most significant prevention measures [8, 10–15]. However, research shows that adequate foot self-care is practiced far too little [11, 16, 17].

In Germany, a few instruments for assessing diabetic self-care are available [18-20]. However, these instruments are neither easy to administer nor focus on foot self-care. Chin and Huang (2013) developed the 7-item Diabetes Foot Self-Care Behavior Scale (DFSBS) specifically for patients with DFS [16]. The original Taiwanese-Chinese version showed evidence of feasibility, validity, and reliability in the target population. An English translation of the Chinese version is available via the original authors. To use the DFSBS within a German-speaking population of patients with DM, a valid and reliable German version needs to be established. Hence, this study aims to translate and cross-culturally adapt the DFSBS from English into German (DFSBS-D) and subsequently evaluate its psychometric properties.

Material and methods

The study was conducted between November 2018 and February 2019 at the Diabetes Center Quakenbrück, department of diabetology, metabolic diseases, and endocrinology at the Christliches Krankenhaus Quakenbrück (CKQ), Medical Campus University of Oldenburg and in a specialized private outpatient chiropody clinic in north-western Germany. Before initiation, the study was reviewed and approved by the Medical Ethical Committee of the School of Medicine, Carl von Ossietzky University Oldenburg (2018–063). In addition, the study was registered at the German Clinical Trials Register (DKRS-ID: DRKS00014962).

Translation and cross-cultural adaptation

The developers of the original DFSBS gave permission to establish a German version of their scale and provided the English version. It was translated into German following a forward-backward procedure as per previous recommendations [21, 22]. First, the original questionnaire was translated into German by two independent translators (T1 and T2) of whom one (T1) was a bilingual resident in internal medicine, while the other (T2) was a German state-approved translator with no medical background. Both translations were synthesized (T12), and a consensus was reached on a preliminary final version. Next, the preliminary German version was tested for wording, phrasing, and understanding in a convenience sample of 12 patients with DM type 1 and type 2. After test-patients’ response evaluation, the research team reached a consensus on cultural adaptation and re-phrasing. Next, a non-medical bilingual individual (BT) blinded to the original DFSBS translated the preliminary DFSBS-D (T12) back into English. Finally, the retranslated version was compared to the initial English questionnaire. Comments on the retranslated version were discussed point-wise with all the involved bilingual translators to find a consensus and incorporate final adjustments to the final German DFSBS-D version.

Participants

Subjects were considered eligible if they (1) were >18 years, (2) suffering from type 1 or 2 DM, and (3) signed written informed consent. Insufficient German language skills or reduced cognitive function to complete the German questionnaire, bilateral leg or foot amputations, and presence of ulcers or wounds precluded participation.

Procedure

Patients were recruited consecutively in a face-to-face manner during their clinic visits. To test the DFSBS-D’s validity and reliability, enrolled patients completed a questionnaire including (1) the newly established DFSBS-D, (2) the German version of the Summary of Diabetes Self-Care Activities Measures (SDSCA-G), (3) the Frankfurter Catalogue of Foot Self-Care-Prevention of the Diabetic Foot Syndrome (FCFSP), and (4) the Short Form Health Survey 36 (SF-36) during their visit. Two weeks after completing the first questionnaire, participants received the DFSBS-D via postal mail and were asked to complete it a second time to determine test-retest reliability. A 2-week interval was considered adequate to assure that clinical change had not occurred [23, 24] and to prevent recall bias. Participants were also requested to evaluate their current state of health concerning their diabetic foot using the simple question: Have there been any changes in your complaints regarding your diabetic feet compared with 2 weeks ago? The question had to be rated dichotomously with either Yes or No. Subjects who reported no changes in complaints were classified as “stable” and their data was used for the reliability analysis [21]. After two weeks, a phone call reminder was used if the re-test questionnaire had not yet been returned.

Measurement instruments

Patient and medical characteristics

The following sociodemographic characteristics were obtained from the self-reported questionnaire: age, sex, height, weight, personal life situation (living alone, with partner and /or children), and educational background (varying from low to high educational levels). Moreover, patients reported the following DM-related information: the number of years diagnosed with DM, type of DM, use of insulin therapy, foot complaints, and kind of foot complaints (e.g., calluses, fissures, or ulcers) if applicable. In addition, patients were asked to provide information about pre-existing comorbidities in the last six months (e.g., vascular disease or PNP).

Diabetes Foot Self-Care Behavior Scale (DFSBS)

The DFSBS is a patient self-reported assessment measuring basic foot self-care routines in patients with DM [16]. The original DFSBS was developed by Taiwanese researchers (Chin and Huang) in 2013 and is available in Chinese and English [16]. The 7-item scale has two parts: the first four items (Part 1) relate to certain DM self-care activities and patients are asked about how many days they had executed those in the past week. In the last three items (Part 2), patients are asked to mark the frequency they perform a particular foot self-care behavior. All responses are rated on a 5-point Likert scale. In part 1, possible answers range from 0 days per week (1), 1–2 days per week (2), 3–4 days per week (3), 5–6 days per week (4) to 7 days per week (5). In part 2, answers vary from never (1) to always (5). The DFSBS total score ranges from 7–35, where higher scores represent better foot self-care behavior [16]. With a Cronbach’s alpha coefficient of 0.73 and an intraclass correlation coefficient of 0.92 after a two-week interval, the original DFSBS’ internal consistency is acceptable, and its test-retest reliability is good. Exploratory factor analysis indicated the DFSBS consists of one factor, explaining 39% of the total sample variance. The DFSBS’s construct validity assessment showed a Pearson’s correlation of 0.45 between the DFSBS and the subscale foot-care of the Chinese version of the diabetes self-care scale and a Spearman’s rho of 0.87 between the DFSBS and the foot-care subscale of The Summary of Diabetes Self-Care Activities Measure [16].

Summary of Diabetes Self-Care Activities Measure (SDSCA-G)

The SDSCA is a brief multidimensional self-report questionnaire of DM self-management. The latest revised version of the English original was released in 2000 and demonstrated good psychometric properties [18, 19, 25]. A German translation (SDSCA-G) was established in 2013 following previous recommendations [18]. The SDSCA-G demonstrated good reliability and validity in a German cohort of patients with DM type 2 [18]. The SDSCA-G consists of 11 items arranged into five subscales, namely (1) general (2 items) and specific (2 items) diet, (2) exercise (2 items), (3) blood-glucose testing (2 items), (4) foot-care (2 items), and (5) smoking (1 item). A Likert scale ranging from 0–7 is provided for each item, which subjects use to indicate the weekly frequency they perform certain self-care behaviors. The mean number of days is calculated for each subscale (except subscale "smoking") and is used to predict and explore subject’s level of self-care [26].

Frankfurter Catalogue of Foot Self-Care (FCFSP)

The FCFSP, developed by Schmidt et al. in 2005, intends to measure disease-related foot self-care behavior in patients with DM to identify and monitor possible deficiencies [20]. It consists of 19 items describing everyday self-care activities a patient with DM should carry out to prevent DFS [20, 27]. The 19 items are divided into three domains: foot self-control (items 1–9), professional assistance in foot-care (items 10–14), and self-control of shoes and socks (items 15–19) [28]. Each item can be answered on a 5-point Likert scale ranging from never (0), seldom (1), sometimes (2), frequently (3), to always (4). A total score and a score for each subscale can be established [29, 30]. Higher total scores indicate better disease-related foot self-care [27, 29, 30]. Total and/or subscale scores close to zero indicate that a patient needs health care professionals’ support to reach adequate daily foot self-care. The FCFSP’s test-retest reliability can be considered acceptable [29, 30]. Although different authors state that the FCFSP was valid [27, 29, 30], no specific data is available to our knowledge.

Short-Form-36-Health Survey (SF-36)

The SF-36 is a self-administered measure to assess subjects’ generic health-related quality of life (HLQoL) [31]. The questionnaire comprises 35 items subdivided into eight dimensions: physical functioning (PF, 10 items), role physical (RP, 4 items), bodily pain (BP, 2 items), general health (GH, 5 items), vitality (VT, 4 items), social functioning (SF, 2 items), role emotional (RE, 3 items) and mental health (MH, 5 items) [32, 33]. One additional item, namely retrospective assessment of health-change over one year, cannot be assigned to a specific item subgroup [32, 33]. Response options are dichotomous (i.e., yes/no) or multiple scaled (i.e., 6-dimension Likert scales). Health-related quality of life is reflected by a sum score calculated from the subscales and converted to a 100-point score, with higher scores representing better health status [34]. The German SF-36 is psychometrically robust for data completeness, validity, and reliability within several populations [31, 34–38].

Statistical analysis

The sample size was chosen to account for a 40% dropout rate and follow the COSMIN guideline. This guideline proposes (1) a minimum number of 100 subjects to assess the internal consistency of health-related patient-reported outcome measures (PROM) and (2) at least 50 subjects of that same sample to evaluate test-retest-reliability [21, 23, 39].

Statistical analysis was performed using IBM®’s Statistical Package for the Social Scientists (SPSS, Version 25; IBM® Corporation, Armonk, NY, USA). Statistical significance was accepted at p≤0.05. Research execution tried to minimize missing values by directly checking each returned questionnaire for data completeness.

Validity

Exploratory factor analysis was used to identify DFSBS-D structural validity [40]. We expected that the DFSBS-D was unidimensional similar to the original DFSBS [16]. An eigenvalue ≥1.0 was defined as an extraction criterion, and factor loadings ≥0.40 were considered to represent a high correlation with the respective factor [41].

To establish construct validity, we established 21 a priori hypotheses regarding the magnitude of the relationship between the DFSBS-D and the SDSCA-G, FCFSP, and SF-36 (Table 3). Construct validity was considered good if at least 75% of the predefined hypotheses were confirmed [23, 42]. Spearman´s correlation coefficients (rs) for the between-instruments relationship were calculated and interpreted according to Domholdt (2000): 0.00 to 0.25 very weak, 0.26 to 0.49 weak, 0.50 to 0.69 moderate, 0.70 to 0.89 strong, and 0.90 to 1.00 very strong correlation [43]. The highest correlation was expected between the DFSBS, the SDSCA-G subscale foot-care, and the FCFSP since their items cover the same construct. Correlations of less than 0.26 were expected to exist between the DFSBS and the SF-36 subscales, as they rather assess two different constructs (Table 3).

Reliability

Stable subjects’ data only were used to establish DFSBS-D reliability. Stable subjects per definition were those patients who reported no change regarding their DM-related foot problems in the re-test questionnaire compared to two weeks earlier. Cronbach’s alpha was calculated to investigate DFSBS-D internal consistency. Values between 0.70 and 0.95 were considered indicating good internal consistency [23]. Test-retest reliability was assessed by calculating two-way random-effects, absolute agreement ICCs with a 95% Confidence Interval (CI). An ICC of ≥0.7 is regarded as good test-retest reliability [21, 42, 44, 45]. We expected the resulting ICCs to be ≥0.7 for both DFSBS subscales [44].

Measurement error was analyzed using standard error measurement (SEM) and minimal detectable change (MDC). The former was calculated with the following formula, using the DFSBS-D total scores’ pooled SD: SEM = SD√1−ICC [21]. The MDC was calculated on an individual level (MDCind) using the following formula: MDCind = 1.96*√2*SEM, while the MDC on group level (MDCgroup) was calculated by dividing the MDCind with √n as per previous recommendations [21, 22]. Bland Altman analysis was used to analyze absolute agreement between the first and second DFSBS-D administration. The mean difference of both administrations accompanied by the 95% CI was calculated. Zero lying between 95% CI of the mean difference was considered absolute agreement, indicating no systematic bias [46]. Limits of agreements (LOA) were defined as the mean difference of both administrations ±1.96 SD(mean difference) [46].

Results

Demographic characteristics

Overall, 150 patients were invited for participation. Of those, 141 (94%) returned the completed questionnaire. However, fifty-nine questionnaires had to be excluded from the final analyses for following reasons: self-reported ulcers or wounds (n = 54), bilateral foot amputations (n = 2), prediabetes (n = 1), self-reported DM type 3 (n = 1), and refusal to continue participation (n = 1). Thus, complete data of 82 subjects were available for final data analyses. Subjects’ demographics are shown in Table 1. The mean age of all participants was 58 ± 15 years, ranging from 20 to 86 years, and 55% were male sex.

Table 1

Demographic characteristics.

Characteristic	Value*
Mean age [years] (n = 82) **	58 ± 15 (20–86)
Sex (n = 82)
Male	45 (55%)
Female	37 (45%)
Mean BMI [kg/m2] (n = 82) **	30.4 ± 6.3 (15.8–49.1)
Living arrangements (n = 82)
Alone	24 (29%)
With partner, and/or children	54 (66%)
Other	4 (5%)
Educational level (n = 82)
Elementary school	37 (45%)
Secondary school	33 (40%)
Higher education	12 (15%)
Type of DM (n = 81)
Type 1	31 (38%)
Type 2	50 (62%)
Mean number of years diagnosed with DM (n = 80) **	15.7 ± 10.9 (0–43)
<10 years	28 (35%)
>10 years	52 (65%)
Insulin treated DM (n = 82)
Yes	66 (80%)
No	16 (20%)

*Values are n (%) unless otherwise specified.

** Mean ± SD (range)

Abbreviations: BMI, body mass index; DM, Diabetes mellitus; n, number of patients; SD, standard deviation

Of these 82 subjects, 52 had been asked to fill in the DFSBS-D a second time for test-retest reliability determination. Fifty subjects (96%) returned the questionnaire fully completed. Forty-eight of these subjects (96%) could be classified as “stable” and thus be included for test-retest reliability analysis. Total scores of the questionnaires are displayed in Table 2.

Table 2

Questionnaire scores.

Scale	Subscale	Value*	SD	Min.	Max.	n
DFSBS-D		21.9	7.6	7	35	82
SDSCA-G	exercise	3.3	1.9	0	7	82
	blood sugar	5.2	2.6	0	7	82
	foot-care	2.6	2.2	0	7	82
FCFSP	self-control of the feet	21.5	9.1	0	36	80
	professional assistance in foot-care	13.7	7.6	0	20	81
	self-control of shoes and socks	11.3	4.8	0	20	81
SF-36	PF	68.4	27.5	0	100	82
	RP	61.0	42.1	0	100	82
	BP	62.0	27.7	0	100	82
	GH	50.4	20.1	0	95	82
	VT	53.4	20.7	0	90	82
	SF	75.8	24.6	0	100	82
	RE	70.3	39.2	0	100	82
	MH	68.4	17.9	8	96	82

*values are mean or sum scores

Abbreviations: DFSBS-D, German version of the Diabetic Foot Self-care Behavior Scale; FCFSP, Frankfurter Catalogue of Foot Self-Care-Prevention of the Diabetic Foot Syndrome; Max., maximal score; Min., minimal score; n = number of patients; SD, standard deviation; SDSCA-G, German version of the Summary of Diabetes Self-Care Activities Measures; SF-36, Short Form Health Survey 36 (PF, physical functioning; RP, role physical; BP, bodily pain; GH, general health; VT, vitality; SF, social functioning; RE, role emotional; MH, mental health)

Validity

Structural validity

A factor analysis was conducted on the seven DFSBS-D items. The total number of factors was based on the initial eigenvalues. Principal component analysis showed one factor with initial eigenvalues greater than 1.0, explaining a cumulative percentage of 57% of the total variance. Item factor loadings ranged from 0.43 to 0.87.

Construct validity

Thirteen (62%) out of 21 predefined hypotheses were confirmed. Spearman correlation coefficients showed correlations ranging from 0.50–0.76 between (items of) the DFSBS-D and items/subscale about foot-care of the SDSCA-G. Correlations between items of the DFSBS-D and FCFSP subscales were lower than hypothesized. The DFSBS-D and the SF-36 subscales showed low correlations as expected. The correlation between the DFSBS-D and the FCFSP subscale self-control of the feet was r = 0.65, which was higher than the correlation between the DFSBS-D and FCFSP subscale self-control of shoes and socks, confirming hypothesis 21. All calculated correlations between the DFSBS-D and the other scales accompanied by a priori hypothesized values are shown in Table 3.

Table 3

Predefined hypotheses and Spearman correlation coefficients.

Scales, subscales, and items compared		Correlation		Confirmation of hypothesis	p-value
		Expected	Spearman
1	DFSBS-D and SDSCA-G subscale foot-care*	>0.70	0.76	Yes	≤.01
2	DFSBS-D item 1 and SDSCA-G item 9	>0.70	0.67	No	≤.01
3	DFSBS-D item 2 and SDSCA-G item 9	>0.70	0.51	No	≤.01
4	DFSBS-D item 6 and SDSCA-G item 10	>0.70	0.76	Yes	≤.01
5	DFSBS-D and FCFSP subscale self-control of the feet**	>0.50	0.70	Yes	≤.01
6	DFSBS-D and FCFSP subscale self-control of shoes and socks***	>0.50	0.62	Yes	≤.01
7	DFSBS-D item 1 and FCFSP subscale self-control of the feet**	>0.70	0.51	No	≤.01
8	DFSBS-D item 2 and FCFSP subscale self-control of the feet**	>0.70	0.47	No	≤.01
9	DFSBS-D item 6 and FCFSP subscale self-control of shoes and socks***	>0.70	0.58	No	≤.01
10	DFSBS-D item 1 and FCFSP item 1	>0.90	0.50	No	≤.01
11	DFSBS-D item 2 and FCFSP item 7	>0.90	0.56	No	≤.01
12	DFSBS-D item 6 and FCFSP item 15	>0.90	0.77	No	≤.01
13	DFSBS-D and SF-36 subscale PF	<0.26	-0.34	Yes	≤.01
14	DFSBS-D and SF-36 subscale RP	<0.26	-0.20	Yes	.06
15	DFSBS-D and SF-36 subscale BP	<0.26	-0.24	Yes	.03
16	DFSBS-D and SF-36 subscale GH	<0.26	-0.21	Yes	.06
17	DFSBS-D and SF-36 subscale VT	<0.26	-0.19	Yes	.08
18	DFSBS-D and SF-36 subscale SF	<0.26	-0.10	Yes	.37
19	DFSBS-D and SF-36 subscale RE	<0.26	-0.24	Yes	.03
20	DFSBS-D and SF-36 subscale MH	<0.26	-0.11	Yes	.33
21	The DFSBS-D is expected to correlate higher with FCFSP subscale self-control than FCFSP subscale shoes			Yes

* SDSCA-G subscale foot-care = SDSCA-G item 9+10;

** FCFSP subscale self-control of the feet = FCFSP item 1–9;

*** FCFSP subscale self-control of shoes and socks = FCFSP item 15–19;

Abbreviations: DFSBS-D, German version of the Diabetic Foot Self-care Behavior Scale; FCFSP, Frankfurter Catalogue of Foot Self-Care–Prevention of the Diabetic Foot Syndrome; SD, standard deviation; SDSCA-G, German version of the Summary of Diabetes Self-Care Activities Measures; SF-36, Short Form Health Survey 36 (PF, physical functioning; RP, role physical; BP, bodily pain; GH, general health; VT, vitality; SF, social functioning; RE, role emotional; MH, mental health)

Reliability

Internal consistency

Cronbach’s alpha of the DFSBS-D was 0.87, indicating good internal consistency.

Test-retest reliability

Test-retest measures are shown in Table 4. The ICC of the DFSBS-D over a two-week time interval was 0.76 (95% CI: 0.60, 0.87), indicating acceptable reliability. Bland Altman analysis showed that zero was lying outside the 95% CI of the mean difference of both administrations (Fig 1), indicating systematic bias. There was no evidence of proportional bias (B = -.115, p = .283).

Table 4

Reliability measures of the DFSBS-D (n = 48).

Measure	Value
First administration mean (±SD)	22.14 (±7.52)
Second administration mean (±SD)	23.56 (±6.79)
Mean difference (95% CI)	1.42 (0.0044, 2.84)
ICC (95% CI)	0.76 (0.60, 0.87)
SEM	2.42
MDCind	6.70
MDCgroup	0.88

Abbreviations: CI, confidence interval; ICC, intraclass correlation coefficient; MDC, minimal detectable change; SD, standard deviation; SEM, standard error of measurement

Fig 1

Bland Altman plot visualizing absolute agreement.

CI = confidence interval; LOA = limits of agreement.

Discussion

The DFSBS was successfully translated and cross-culturally adapted into German (DFSBS-D). The results indicate that the DFSBS-D has good structural validity, internal consistency, and test-retest reliability. However, construct validity appears to be questionable.

The DFSBS has until now only been available in a Chinese version, which was validated for Taiwan [16]. In addition, an English version was composed from the Chinese questionnaire. However, to our knowledge measurement properties of the English version have not yet been established [16]. Therefore, all results regarding the DFSBS-D found in the present study can only be compared with those of the original Chinese DFSBS version.

The DFSBS-D’s structural validity can be considered good. Based on the results of the principal component analysis, the DFSBS-D has a one factor structure, explaining 57% of the total sample variance. While Chin and Huang (2013) determined two factors with eigenvalues greater than 1.0 for the original DFSBS, only one factor was above the scree plot’s elbow [16]. Thus, based on the scree plot, the developers set the number of factors to one and considered the original 7-item DFSBS also as unidimensional [16]. The one factor of the original DFSBS explained only 39% of the total sample variance, which is somewhat lower compared to the DFSBS-D. Overall, the results regarding the structural validity of the DFSBS-D are in line with those of the original version.

The construct validity of the DFSBS-D can be considered questionable since only 62% of the 21 predefined hypotheses were confirmed. The COSMIN guidelines recommend that at least 75% of predefined hypotheses must be confirmed to indicate sufficient construct validity [23, 42]. The a-priori set hypotheses concerned the expected correlation between the scores on the DFSBS-D and those of other scales measuring (1) self-care behavior in patients with DM (SDSCA-G), (2) foot self-care behavior in patients with DM (FCFSP), as well as (3) health status and generic health-related quality of life (SF-36). Except for the SDSCA, all other questionnaires have not been used for hypotheses testing of the DFSBS before. Therefore, the predefined hypotheses of the FCFSP and the SF-36 were theoretically derived and not based on available research findings regarding the DFSBS in other languages. In addition, the lack of information about the validity and reliability of the German-language FCFSP must be considered. This may explain the 38% rejected hypotheses, especially regarding correlations between the DFSBS-D and the FCFSP.

We found a high correlation (r = 0.71) between the DFSBS-D and SDSCA-G subscale foot-care. That met our expectations as both scales measure a similar construct. Chin and Huang (2013) also indicated a high positive correlation (r = 0.87) between the original DFSBS and the SDSCA subscale foot care [16]. Consequently, we conclude that, based on correlations between the DFSBS-D and SDSCA subscale foot-care and the consistency with previous findings during the validation process of the original DFSBS, the construct of the DFSBS-D is valid.

Regarding the SF-36, it could be speculated that fewer health issues in patients suffering from DM result from better (foot) self-care, leading to greater HRQoL in the respective patient cohort. According to Bonner et al. (2016) and Grady et al. (2011), HRQoL of patients with DM type 2 would increase with the implementation of a more comprehensive self-management education [47, 48]. Nonetheless, since the interdependence of foot self-care and HRQoL is yet unknown, only weak correlations were expected to exist between the DFSBS-D and the SF-36. That was indeed confirmed in the current results, where correlations between the DFSBS-D and all SF-36 subscales were very weak (r <0.26).

In general, evaluating measurement properties based on total scores or subscales of an instrument is preferred compared to an item-based evaluation [42]. Yet, as the DFSBS-D has only seven items and no subscales, and following the COSMIN guidelines, at least ten hypotheses should be formulated for validity testing [23], we included six item-based hypotheses. In retrospect, these item-based hypotheses might have been too detailed. On the other hand, they almost scored the expected correlations. Furthermore, they provide relevant information about the measured construct.

The present study results suggest that the DFSBS-D is a reliable patient self-reported instrument. The DFSBS-D’s internal consistency (Cronbach’s alpha = 0.84) was slightly higher than that of the original DFSBS (Cronbach’s alpha = 0.73) [16]. Test-retest reliability of the DFSBS-D (ICC = 0.73) can be interpreted as good [21, 44, 45]. This is in contrast to the original DFSBS, which showed an excellent test-retest reliability (ICC 0.92) over a 2-week interval [16]. However, the ICC is sample-dependent [21]. Thus, the differences in test-retest reliability may be explained by minor differences (e.g., cultural differences) between the current sample and the one of Chin and Huang (2013) [16].

Despite the DFSBS-D’s high internal consistency and acceptable test-retest reliability, a systematic bias cannot be entirely ruled out, as witnessed from the Bland and Altman plot (Fig 1). Subjects scored on average 1.78 points higher on the DFSBS-D during the second administration, which might be explained by a better foot self-care behavior initiated by the first DFSBS-D administration.

Self-report measures produce larger measurement errors in general, according to Field (2018), because additional factors influence how people respond [40]. Nevertheless, the relatively high measurement error (SEM 2.54 and MDCind 7.04) indicates that the DFSBS-D may not be an appropriate instrument to monitor changes between two or more different measurement time points [21, 40]. A minimum difference as high as the MDCind is required to indicate that an actual change has occurred between two assessments of an individual [21, 40]. This is relatively high considering that the DFSBS-D total score varies between 7–35. Regarding group comparison, a difference of the DFSBS-D mean scores larger than the MDC on group level (MDCgroup) would speak for an actual between-group difference. However, differences in scores smaller than the SEM cannot rule out measurement error. Therefore, a difference of at least 2.54 is required to detect a statistically significant difference between two DFSBS-D scorings. Since no minimal important change (MIC) values were assessed in this study, it is unclear whether this indicates a clinically relevant difference. To determine the DFSBS-D’s MIC further research is required [21].

The number of subjects used for establishing the DFSBS-D’s psychometric properties were somewhat smaller (n = 82) than those recommended by the COSMIN panel (n = 100) and initially strived for. However, a subject-to-item ratio of 10:1 is also regarded sufficient for scale validation purposes [45] and as the DFSBS-D consists of seven items, the sample analyzed was still large enough to provide trustworthy results. With respect to test-retest reliability we only missed the targeted number of subjects (n = 50) by two subjects.

Conclusion

The original DFSBS was successfully translated and culturally adapted into a German version (DFSBS-D). This study’s results suggest that the DFSBS-D’s psychometric properties are good in terms of structural validity, internal consistency, and test-retest reliability. Construct validity appeared to be questionable at first sight. However, a more in-depth interpretation of the results assumes that the DFSBS-D’s construct validity is sufficient. Overall, we conclude that the DFSBS-D is a valid and reliable instrument to assess foot self-care behavior in German-speaking patients with DM type I and II. Future studies are warranted to determine the DFSBS-D’s applicability regarding patients with and without PNP and/or POAD, as these are the two main underlying pathologies of the DFS [49].

DFSBS-D questionnaire.

(PDF)

Click here for additional data file.

8 Mar 2022

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Reviewer #1: Diabetes foot self-care is a vital part of overall management of both Type 1 and 2 Diabetes. The consequences of foot pathology are extremely serious both to the patient and the health economy. Prevention of foot pathologies, including the vital part played by self-care, are extremely important.

The authors make the point that for diabetes foot syndrome prevention a valid and reliable instrument for measuring daily foot care routines in patients with diabetes is required but no such instruments are available in the German language. Their study aim was to translate and interculturally adapt the Diabetes Foot Self-Care Behaviour Scale (DFSBS) into a German language version (DFSBS-D)and evaluate its validity and reliability. They used accepted and validated methods to translate and validate the DFSBS in the German language and test its reliability. They report the successful translation into German with structural validity, test-retest reliability and internal consistency although they suggest that "construct validity" may be debated. I have just a few minor comments:

1. Their final numbers were less than recommended by COSMIN Guidelines. Do the authors have concerns about this and perhaps this could be explored in their Discussion.

2. Was their any suggestion of a difference in their findings between patients with Type 1 or Type 2 Diabetes or indeed between those on insulin and not on insulin? I realise numbers become relatively small when they try to do this.

3. I'm not keen on their terminology in Table 1 when they refer to "Insulin depended diabetes". There are lots of reasons for people being put on insulin. It would be simpler to use the term "Insulin treated diabetes"

4. It is not considered politically correct these days to talk about "diabetic patients" etc. It is better to use the designation "people/patients with diabetes"-this terminology needs looking at throughout the paper.

5. At no point do the authors clearly state what language they translated from! The original publication was in Chinese. I assume their translation was from the English version. Is that correct? Please add this in the manuscript.

The authors are to be congratulated in producing what appears to be an important development in the diabetes foot self-care management in the German language. My points are minor and overall I was most impressed by this study.

Reviewer #2: The authors have provided a technically sound paper presented in an intelligible fashion assessing the validity and reliability of the German translation of the DFSBS-D. The data do support the conclusions reported in the manuscript and the statistical analyses have been performed appropriately/rigorously with a few comments as described below.

Abstract:

Materials and Methods section: n=82 for the assessment of construct reliability but for test-retest reliability only stable patients n=48 participants assessed (2-weeks between baseline and the 2nd visit). Differences between the “stable” n=48 participants?

Materials and Methods:

• Procedure section: For the test-retest were there differences on anything between those who completed the baseline vs. those who were included in the test-reliability analyses? How many people did not return the questionnaire? Differ3ences on those people as well?

• Statistical Analysis section page 8 line 180-181: what did researchers do with the missingness? Ignore it or some sort of missingness approach?

• Validity Statistical Analysis section: good included interpretation of factor loadings considered high and interpretations of spearman correlation coefficients considered high to weak

• Reliability Statistical Analysis section: were there differences between those who were not included in the test-retest, or those who were not stable as indicated by saying “yes”, any differences in those who did not answer at all ?

Results:

• As mentioned above, were there any differences in the individuals who returned the questionnaire and were categorized as stable/used for the test-retest analyses vs. those who did not say they were stable or did not return the questionnaire?

o If ALL individuals who returned the questionnaires (including those who were not defined as “stable”) did the test-retest results change? Or were they similar?

• Page 13 lines 263-265 (Figure 1). What was the Pearson correlation coefficient for the Bland-Altman analyses? That is the correlation between the differences and means? Was this Pearson correlation coefficient significant? If no you could state there was not proportional biases were observed. Yes, this 0-value is outside the confidence intervals but I would also include the Pearson correlation coefficient/p-value between the differences/means as that will be a good indicator of if there truly was systematic bias.

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4 May 2022

PLOS ONE

Review Manuscript: PONE-D-22-05239

Manuscript Title: Validity and reliability of the German translation of the Diabetes Foot Self-Care Behavior Scale (DFSBS-D)

Oldenburg, 04-06-2022

Re-submission due date: 04-07-2022

Response to Reviewers

Editor’s comment 1:

Journal Requirements:

When submitting your revision, we need you to address these additional requirements.

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2. PLOS ONE has specific requirements for studies that are presenting a new method or tool as the primary focus, including a newly developed or modified questionnaire or scale (https://journals.plos.org/plosone/s/submission-guidelines#loc-methods-software-databases-and-tools.) One requirement is that the questionnaire or scale must be openly available under a license no more restrictive than CC BY. In light of this, before we proceed, please include a copy of your questionnaire or scale as a Supporting Information file or provide a link if it is available through an online repository. Also, in your Methods section, please discuss whether you obtained the necessary permissions from the owner of the original questionnaire to modify it.

Authors’ response: Thank you very much for making us aware about not having followed the correct file naming convention during submission. We now changed this in accordance with the PLOS formatting guidelines. Moreover, we appreciate the journal requires new tools to be publicly accessible. Actually, a copy of the German DFSBS version had already been part of the initial submission as a supplementary file. Nevertheless, we are happy to once again upload a copy together with the revised documents. What we indeed were missing in our initial submission was the original authors official permission to establish a German version of their questionnaire. The e-mail from Dr. Chin is now included in the revised documents as per your request. We also included a sentence in the methods section that the permission to modify the original DFSBS into a German version was obtained from the developer (Lines 79-80)

3. In your Data Availability statement, you have not specified where the minimal data set underlying the results described in your manuscript can be found. PLOS defines a study's minimal data set as the underlying data used to reach the conclusions drawn in the manuscript and any additional data required to replicate the reported study findings in their entirety. All PLOS journals require that the minimal data set be made fully available. For more information about our data policy, please see http://journals.plos.org/plosone/s/data-availability.

"Upon re-submitting your revised manuscript, please upload your study’s minimal underlying data set as either Supporting Information files or to a stable, public repository and include the relevant URLs, DOIs, or accession numbers within your revised cover letter. For a list of acceptable repositories, please see http://journals.plos.org/plosone/s/data-availability#loc-recommended-repositories. Any potentially identifying patient information must be fully anonymized.

Important: If there are ethical or legal restrictions to sharing your data publicly, please explain these restrictions in detail. Please see our guidelines for more information on what we consider unacceptable restrictions to publicly sharing data: http://journals.plos.org/plosone/s/data-availability#loc-unacceptable-data-access-restrictions. Note that it is not acceptable for the authors to be the sole named individuals responsible for ensuring data access.

We will update your Data Availability statement to reflect the information you provide in your cover letter.

Authors’ response: We appreciate PLOS One’s policy to provide full open access to the underlying dataset whenever possible. However, after consultation with the responsible data protection officer, publication of our underlying dataset in an open/public repository or supplementary file is not possible due to the strict data protection guidelines in Germany. In our informed consent we did not specifically ask participants for permission to publicly upload their data. We did not even address such a public upload could be a possibility during the publication process. Thus, participants did not consent to open publication of their data when joining the study. From an ethical and data privacy/protection standpoint we should have at least informed the participants about the possibility of an open publication of the study-related database, what we unfortunately failed to do. Therefore, a de-identified minimal dataset used and analyzed for this manuscript can only be made available to other researchers on reasonable request by sending an email to the research unit of the University Hospital for Orthopeadics and Trauma Surgery Pius-Hospital, Medical Campus University of Oldenburg (orthopaedie.pius@uni-oldenburg.de).

Reviewer 1 comments:

General comment:

Diabetes foot self-care is a vital part of overall management of both Type 1 and 2 Diabetes. The consequences of foot pathology are extremely serious both to the patient and the health economy. Prevention of foot pathologies, including the vital part played by self-care, are extremely important.

The authors make the point that for diabetes foot syndrome prevention a valid and reliable instrument for measuring daily foot care routines in patients with diabetes is required but no such instruments are available in the German language. Their study aim was to translate and interculturally adapt the Diabetes Foot Self-Care Behaviour Scale (DFSBS) into a German language version (DFSBS-D) and evaluate its validity and reliability. They used accepted and validated methods to translate and validate the DFSBS in the German language and test its reliability. They report the successful translation into German with structural validity, test-retest reliability and internal consistency although they suggest that "construct validity" may be debated. I have just a few minor comments:

Reviewer 1 Comment 1

1. Their final numbers were less than recommended by COSMIN Guidelines. Do the authors have concerns about this and perhaps this could be explored in their Discussion.

Authors’ response: We appreciate you are raising this question. Due to the relatively large number of patients that unfortunately had to be excluded due to self-reported foot ulcer and or amputations as outlined in the manuscript, we indeed failed to reach the subject number we initially strived for. However, we think that our analyzed sample still is large enough to provide trustworthy results. In fact, there is an ongoing debate as to how many subjects are required at a minimum for PROM validation (Terwee et al 2007). Next to the suggested minimum of 100 subjects, another accepted rule of thumb is to include a subject-to-item ratio of 10:1 (Nunally & Bernstein 1994). Thus, as the DFSBS presents with only 7 items in total, a minimum of 70 subjects would actually still be sufficient for establishing psychometric properties. Concerning test-re-test reliability we were able to analyze 48 stable subjects. Thus, we missed the targeted number of n=50 by only two subjects, what we think is still acceptable. Nevertheless, we see your point that we should address this aspect in the discussion and included a statement as per your suggestion (Lines 343-348).

References:

Terwee CB, Bot SD, de Boer MR, et al. Quality criteria were proposed for measurement properties of health status questionnaires. J Clin Epidemiol. 2007;60(1):34-42.

Nunally JC, Bernstein IH. Psychometric Theory. 3rd ed. New York, NY: McGraw-Hill 1994.

Reviewer 1 Comment 2

2. Was there any suggestion of a difference in their findings between patients with Type 1 or Type 2 Diabetes or indeed between those on insulin and not on insulin? I realize numbers become relatively small when they try to do this.

Authors’ response: Thank you for asking this question. However, we did not investigate into this as indeed our numbers would not have reached the minimal recommended subject-to-item ratio anymore to produce valid and reliable results. The DFSBS-D intents to evaluate daily foot-care routines in terms of a preventive measure in patients with DM. As it is about prevention, one could assume it is not primarily important which type of diabetes one is diagnosed with or whether one is receiving insulin or not as all patients diagnosed with DM should develop a regular foot self-care routine for foot ulcer prevention. Whether there is a difference in adherence to the recommended preventive foot-care depending on the diagnosed type of diabetes or insulin treatment could be evaluated in future studies.

Reviewer 1 Comment 3

3. I'm not keen on their terminology in Table 1 when they refer to "Insulin depended diabetes". There are lots of reasons for people being put on insulin. It would be simpler to use the term "Insulin treated diabetes"

Authors’ response: We appreciate your suggestion and changed the wording in Table 1 accordingly.

Reviewer 1 Comment 4

4. It is not considered politically correct these days to talk about "diabetic patients" etc. It is better to use the designation "people/patients with diabetes"-this terminology needs looking at throughout the paper.

Authors’ response: Thank you for this comment. Our intend for using the phrase “diabetes patient” instead of “patient with diabetes” was merely to skimp on prepositions and ease reading. However, we appreciate your thought about politically correct language use. Thus, we changed the wording throughout the manuscript as per your suggestion.

Reviewer 1 Comment 5

5. At no point do the authors clearly state what language they translated from! The original publication was in Chinese. I assume their translation was from the English version. Is that correct? Please add this in the manuscript.

Authors’ response: Thank you for raising this aspect. We indeed translated the English version of the DFSBS, which was provided by the original authors. We added this information to the abstract (Line 30) and the introduction (Lines 66 and 69) as well as to the Material and Methods (Line2 79-80) section.

Reviewer 1 Comment 6

The authors are to be congratulated in producing what appears to be an important development in the diabetes foot self-care management in the German language. My points are minor and overall I was most impressed by this study.

Authors’ response: Thank you.

Reviewer 2 comments:

General comment:

The authors have provided a technically sound paper presented in an intelligible fashion assessing the validity and reliability of the German translation of the DFSBS-D. The data do support the conclusions reported in the manuscript and the statistical analyses have been performed appropriately/rigorously with a few comments as described below.

Reviewer 2 Comment 1

Abstract:

Materials and Methods section: n=82 for the assessment of construct reliability but for test-retest reliability only stable patients n=48 participants assessed (2-weeks between baseline and the 2nd visit). Differences between the “stable” n=48 participants?

Authors’ response: Thank you very much for this question. However, we are not quite sure what exactly you refer to. Data from all 82 eligible subjects were used to establish construct validity (not “construct reliability” as the reviewer mentions). In order to evaluate test-retest reliability we had consecutively send out the DFSBS-D to 52 of the 82 enrolled subjects again, asking them to fill it in a second time. Only data from those patients who answered the question “Have there been any changes in your complaints regarding your diabetic feet compared with 2 weeks ago?” accompanying the re-test questionnaire with “no” were used for the test-retest reliability analysis as per previous recommendations (de Vet et al 2018, Mokkink et al 2010). From n=50 subjects who returned their fully completed re-test questionnaire, n=48 indicated no change and thus got the attribute “stable”. A test-retest reliability analysis is not about how a scale measures a specific construct. Instead, it intends to evaluate the extent to which the scores (here: DFSBS-D scores) for subjects that had not changed over time regarding the measured construct were the same for repeated measures (de Vet et al 2018, Mokkink et al 2010). In that sense, using data from patients who indicate to have changed from the first questionnaire administration to the second does not make sense. We hope this addresses your question sufficiently. Otherwise, we would appreciate to learn more about what exactly you mean with “differences between stable participants”.

References:

De Vet HCW, Terwee CB, Mokkink LB, et al. Measurement in Medicine: practical guides to biostatistics and epidemiology. Cambridge, UK: Cambridge University Press 2018.

Mokkink LB, Terwee CB, Patrick DL, et al. The COSMIN study reached international consensus on taxonomy, terminology, and definitions of measurement properties for health-related patient-reported outcomes. J Clin Epidemiol. 2010;63(7):737-45.

Reviewer 2 Comment 2

Materials and Methods:

• Procedure section: For the test-retest were there differences on anything between those who completed the baseline vs. those who were included in the test-reliability analyses? How many people did not return the questionnaire? Differences on those people as well?

Authors’ response: Thank you for this question. We will try to explain that in more detail. As we describe in the methods section, initially 150 patients were consecutively invited for study participation. Of these 141 returned a completed questionnaire. Re-tests were sent out in a consecutive manner to patients who had completed the first DFSBS-D and we stived for at least n=50 stable subjects for the test-retest reliability analysis. Overall, we have sent out 116 consecutive re-tests and n=75 subjects returned them of which n=58 were categorized as “stable”. Thus, we stopped sending out more re-tests at this time point. However, as described in the demographic characteristics section of the manuscript, n=59 subjects had to be excluded leaving n=82 subjects for this study’s analyses. Fifty-two of these n=82 subjects were among the patients that had been provided with a re-test before we stopped sending out re-tests. Thus n=30 out of the n=82 subjects had not gotten a re-test. Response of those who got a retest (n=52) was 100%. However, two (n=2) of the n=52 subjects did not fill in the re-test due to unknown reasons but instead returned it blank, leaving n=50 subjects that returned their re-test questionnaire fully completed. Two (n=2) of these n=50 subjects, however, indicated to have changed over time, thus leaving n=48 “stable” subjects, whose data could be used for the test-retest analysis.

Concerning your question about any differences between those subjects who returned their re-test vs. those who did not, we already mentioned that all 52 subjects returned their re-test. Moreover, there were no significant differences (p>.05) between the n=2 “changed” subjects versus the n=48 “stable” subjects – neither with regard to demographic characteristics nor for the questionnaire scores. In addition, no significant differences (p>.05) could be found between the n=30 subjects who did not receive a re-test anymore versus the n=52 who did.

• Statistical Analysis section page 8 line 180-181: what did researchers do with the missingness? Ignore it or some sort of missingness approach?

Authors’ response: We appreciate your question. We indeed tried to follow up with the patients about any missing items. However, two patients could not recall when they were first diagnosed with DM and one patient who missed to fill in the diagnosed type of DM was unfortunately not accessible anymore due to incorrect contact data. With regard to the FCFSP only four items in total were missing (two items in subscale “Self-control of the feet” and one item each in the subscales “professional assistance in foot-care” and “self-control of shoes and socks”, respectively). Here, we also tried to follow-up on the missing items. However, in the list of our questionnaires, the FCFSP was the last one to fill in. When asked about the missing items, the respective patients refused to answer these as they felt they had already answered the same/a very similar question in one of the previous questionnaires and thus rejected to answer due to self-perceived redundancy even though we explained the necessity of complete data for each questionnaire. Subsequently, in order to avoid possible distortion of FCFSP subscale results in response to a missing item, we only included subjects with complete data in the respective subscale analysis.

• Validity Statistical Analysis section: good included interpretation of factor loadings considered high and interpretations of spearman correlation coefficients considered high to weak

Authors’ response: Thank you.

• Reliability Statistical Analysis section: were there differences between those who were not included in the test-retest, or those who were not stable as indicated by saying “yes”, any differences in those who did not answer at all?

Authors’ response: Thank you for that question. As described in our previous response to the second comment of Reviewer 2 (please see above), re-tests were sent out consecutively and just stopped at a certain time point. There were no statistically significant differences (p>.05) regarding demographic characteristics or questionnaire scores between (1) subjects that were provided with the re-test questionnaire versus those who were not or (2) subjects that were included in the test-retest reliability analysis (i.e., n=48 stable subjects) vs. those who were not (i.e., n=2 changed subjects). The only difference between “stable” versus “changed” subjects was that stable subjects’ foot-related complaints had not changed over time versus a self-reported change over time in foot-related complaints in the “changed” subjects.

Reviewer 2 Comment 3

Results:

• As mentioned above, were there any differences in the individuals who returned the questionnaire and were categorized as stable/used for the test-retest analyses vs. those who did not say they were stable or did not return the questionnaire?

Authors’ response: Thank you for raising that aspect again. As described in our response to the second comment of Reviewer 2 (please see above), there were no statistically significant differences (p>.05) between the n=2 “changed” subjects versus the n=48 “stable” subjects – neither with regard to demographic characteristics nor for the questionnaires. The only difference between “stable” versus “changed” subjects was that “stable” subjects’ foot-related complaints had not changed during both questionnaire administration timepoints while those of the “changed” patients did. As we were only interested in whether subjects were “stable” or not (i.e., whether their data can be used for test-retest reliability analysis or not) we did not ask for specific details of any change in complaints. Hence, we are not able to report what kind of changes in complaints occurred in the n=2 “changed” subjects as this was beyond the scope of this study.

o If ALL individuals who returned the questionnaires (including those who were not defined as “stable”) did the test-retest results change? Or were they similar?

Authors’ response: We appreciate your question. However, we did not analyze this. The aim of a test-retest reliability testing is to find out about the degree to which a measurement is free from measurement error. Thus, it is about reproducibility or, in other words, it aims at finding out to what extent the score for subjects that had not changed over time were the same for repeated measures (de Vet 2018). Thus, taking data from subjects into account who indicate changes in complaints from the first to the second questionnaire administration is not reasonable. Therefore, for a test-retest reliability analysis one only takes into account results from “stable” patients as described in the manuscript. Otherwise, the calculated coefficient is not valid.

• Page 13 lines 263-265 (Figure 1). What was the Pearson correlation coefficient for the Bland-Altman analyses? That is the correlation between the differences and means? Was this Pearson correlation coefficient significant? If no you could state there was not proportional biases were observed. Yes, this 0-value is outside the confidence intervals but I would also include the Pearson correlation coefficient/p-value between the differences/means as that will be a good indicator of if there truly was systematic bias.

Authors’ response: Thank you for that suggestion. As the DFSBS-D differences were not statistically different (p>.05), we run a linear regression analysis on the data to verify the absence of proportional bias as per your suggestion. The regression coefficient of the DFSBS-D mean was B=-0.115 with an accompanying insignificant p = .283. This indicates that there is no trend where there are more data points above or below the mean difference line that one would like to see. Thus, bias was truly systematic instead of proportional. We included this information in the results section (Line 264).

Submitted filename: Response to Reviewers.docx

Click here for additional data file.

20 May 2022

Validity and reliability of the German translation of the Diabetes Foot Self-Care Behavior Scale (DFSBS-D)

PONE-D-22-05239R1

Dear Dr. Seeber,

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.

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Academic Editor

PLOS ONE

Additional Editor Comments (optional):

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: All comments have been addressed

Reviewer #2: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

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: (No Response)

Reviewer #2: All additional concerns and questions have been addressed. The manuscript is much improved compared to the original version.

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Reviewer #1: Yes: Anthony Howard Barnett

Reviewer #2: No

24 May 2022

PONE-D-22-05239R1

Validity and reliability of the German translation of the Diabetes Foot Self-Care Behavior Scale (DFSBS-D)

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