Financial incentives to increase stool collection rates for microbiome studies in adult bone marrow transplant patients.

INTRODUCTION: In order to study the role of the microbiome in hematopoietic stem cell transplantation (HCT), researchers collect stool samples from patients at various time points throughout HCT. However, stool collection requires active subject participation and may be limited by patient reluctance to handling stool.
METHODS: We performed a prospective study on the impact of financial incentives on stool collection rates. The intervention group consisted of allogeneic HCT patients from 05/2017-05/2018 who were compensated with a $10 gas gift card for each stool sample. The intervention group was compared to a historical control group of allogeneic HCT patients from 11/2016-05/2017 who provided stool samples before the incentive was implemented. To control for possible changes in collections over time, we also compared a contemporaneous control group of autologous HCT patients from 05/2017-05/2018 with a historical control group of autologous HCT patients from 11/2016-05/2017; neither autologous HCT group was compensated. The collection rate was defined as the number of samples provided divided by the number of time points we attempted to obtain stool.
RESULTS: There were 35 allogeneic HCT patients in the intervention group, 19 allogeneic HCT patients in the historical control group, 142 autologous HCT patients in the contemporaneous control group (that did not receive a financial incentive), and 75 autologous HCT patients in the historical control group. Allogeneic HCT patients in the intervention group had significantly higher average overall collection rates when compared to the historical control group allogeneic HCT patients (80% vs 37%, p<0.0001). There were no significant differences in overall average collection rates between the autologous HCT patients in the contemporaneous control and historical control groups (36% vs 32%, p = 0.2760).
CONCLUSION: Our results demonstrate that a modest incentive can significantly increase collection rates. These results may help to inform the design of future studies involving stool collection.

Introduction

The human gut microbiome is the myriad of bacteria, archaea, viruses, and fungi that reside in the human gastrointestinal tract [1-3]. In hematopoietic stem cell transplantation (HCT), disruption of the gut microbiome, concomitant of the transplant conditioning regimen, is associated with post-transplant complications such as the development of graft-versus-host disease and infections [4, 5]. Although many strides have been made in investigating the complex relationship between the gut microbiome and its host, further elucidation of the role of the microbiome in patients undergoing HCT is essential in order to improve patient outcomes [1]. The gut microbiome can be studied with next-generation sequencing of microbial nucleic acids that are extracted from human stool samples [2, 6].

Despite knowing how to utilize human stool samples to investigate the microbiome, we have found that the challenge lies in collecting enough stool samples from study participants at various time points throughout the transplant process. Paramsothy et al. found that this challenge exists even when requesting stool samples from healthy donors, demonstrating that approximately 40% of potential donors declined to participate in their study due to the burden of providing stool samples over a six-week period [7]. A different study focused on at-home stool collection, specifically in cancer patients, by Hogue et al. revealed that only 58% of consented patients provided baseline stool samples and only 25% of consented patients provided follow-up stool samples [8]. Unlike other human tissue sampling methods such as drawing blood or swabbing the skin, collecting stool involves more effort on behalf of the patients, especially in the outpatient setting where patients must handle the stool themselves before subsequently placing in a specimen cup [9]. Thus, stool collection compliance in research studies may be hindered as a result of patient apprehension to handling stool due to factors such as embarrassment, disgust, and privacy concerns [10-12]. Furthermore, cancer patients may experience weakness or constipation due to treatment, which can result in noncompliance with stool collection protocols [8].

However, financial incentives may motivate patients to be more willing to provide stool samples, thus leading to increased adherence to study protocols. For example, Green et al. found that both a modest incentive of $10 and a probabilistic incentive of a 10% chance of winning $50 significantly increased rates of another stool-related research activity, fecal immunochemical testing ($10 incentive 73.3% vs 66.2%, p = 0.04; chance of winning 71.8% vs 66.2%, p = 0.04), despite not increasing colorectal cancer screening via colonoscopy [9, 13]. Incorporating a strategy that includes financial incentives into a research study design can significantly increase the desired outcome [14-16]. Therefore, we believed that we could significantly improve study participant compliance to providing stool samples throughout the HCT process by giving them compensation for their stool samples.

Materials and methods

This study was approved by the Duke Health Institutional Review Board (IRB), and written informed consent was obtained from all study participants (IRB protocol #Pro00006268 and Pro00078566).

Defining groups and sample collection

Patients in the intervention group were compensated financially for their stool samples. The intervention group was composed of patients undergoing allogeneic HCT with treatment start dates between 05/11/2017, the date when the financial incentive was implemented, and 05/11/2018. Collection rates, in addition to baseline characteristics, of the allogeneic HCT patients in the intervention group were compared to those of allogeneic HCT patients from a historical control group. The historical control allogeneic HCT patients had treatment start dates between 11/10/2016, the date a study team member started actively managing stool collection in patients through distribution of collection coolers and consistent follow-up, and 05/10/2017. The allogeneic HCT patients in the historical control group were not compensated.

In order to control for potential differences in stool collection over two different time periods, a contemporaneous control group was also included in the study design. The contemporaneous control group consisted of patients undergoing autologous HCT with treatment start dates between 05/11/2017 and 05/11/2018 who were not compensated in any way for their stool samples. Collection rates and baseline characteristics of the autologous HCT patients in the contemporaneous control group were compared to those of autologous HCT patients from a historical control group. The historical control autologous HCT patients had treatment start dates between 11/10/2016 and 05/10/2017, and these patients were not compensated in any way for their stool samples. Of note, no autologous HCT patients, regardless of control group, were compensated in this study; only the allogeneic HCT patients from the intervention group were compensated. Regardless of group, if a patient’s HCT treatment start date fell outside of the specified date ranges for a group, this patient was not included in the final analysis in order to prevent overlap between groups.

In this prospective cohort study, allogeneic HCT patients in both the intervention group and the historical control group were required to provide stool samples at the following time points throughout the HCT process: pre-HCT, day 0 (the day of HCT), and days 7, 14, 21, 30, 60, and 90 post-HCT. Since autologous HCT patients do not come to the Adult Blood and Marrow Transplant Clinic as frequently as allogeneic HCT patients, autologous HCT patients in both the contemporaneous control group and the historical control group were only required to provide stool samples at the following time points throughout the HCT process: pre-HCT and days 7, 14, and 90 post-HCT. Fig 1 provides an overview of the study, depicting group comparisons and when samples were collected from each group.

Fig 1

Sample collection timeline for all groups.

Allo collection schedule: Pre-HCT → Day 0 → Day 7 → Day 14 → Day 21 → Day 30 → Day 60 →Day 90. Auto collection schedule: Pre-HCT → Day 7 → Day 14 → Day 90.

Stool samples were categorized as “inpatient” if scheduled to be provided by the patient while admitted to the hospital at the time of sample collection or “outpatient” if not admitted at the time of sample collection. When samples were collected in the outpatient setting, the patient was provided with a stool collection kit comprised of a stool collection hat, a specimen cup, a tongue depressor, and a pair of gloves, along with a cooler and ice pack to store the sample after collecting it themselves. In the inpatient setting, nurses provided patients with a stool collection hat, but the nurses were the ones that performed all the steps of collection and storage after defecation. Patients in the intervention group were allocated a $10 gas gift card for each stool sample provided regardless of whether stool was collected in the inpatient or outpatient setting.

Data collection

Stool collection was tracked by assessing the number of samples given at their required time points. A collection probability was delineated as the number of samples actually provided by the participant divided by the number of time points for which we required samples be provided. The Duke Adult Blood and Marrow Transplant database was used to query the exact dates that stool samples were collected from each patient in order to verify that samples were provided at the required time points. Only stool samples given between 05/11/2017 and 05/11/2018 were accounted for when determining collection rates for both the intervention and contemporaneous control groups whereas only stool samples given between 11/10/2016 and 05/10/2017 were accounted for when determining collection rates for the historical control group. If a sample was given outside of these time frames, the sample was not included when determining the collection rate. Thus, if a time point typically requiring a sample be given fell outside of these time frames, that time point was not included when assessing compliance, neither hurting the participant’s collection rate if no sample was given, nor helping the participant if a sample was given. Furthermore, if a participant withdrew from the study or died, then the subsequent time points after date of death or withdrawal were not included in the analysis. Each sample was tracked for whether it was provided in the inpatient or outpatient setting in order to assess inpatient and outpatient collection rates. Demographic data such as age, gender, race, ethnicity, disease, and conditioning type were abstracted from the Duke Adult Blood and Marrow Transplant database and from electronic medical records.

Statistical analysis

Baseline demographics were summarized with N (%) for categorical variables and median (interquartile range) with mean (standard deviation) for continuous variables for all patients. Chi-square tests or Fisher’s exact tests were utilized to compare categorical variables, as appropriate, and Wilcoxon Rank Sum tests or t-tests were utilized to compare continuous variables, as appropriate. For allogeneic patients, negative binomial regression with generalized estimating equation (GEE) was performed to model the inpatient and outpatient collection rates of each patient, if applicable. GEE with compound symmetry correlation structure was used to account for the correlation of the two rates for each patient. Other covariates such as age, gender, race, disease, and conditioning type were adjusted for in order to avoid confounding. All analyses were conducted using SAS version 9.4 (SAS Institute, Cary, NC) and R version 3.5.0.

A priori sample size calculation was not performed for this study. While this study was approved by the Duke Health IRB and written informed consent was obtained from all study participants, this study was not formally planned.

Results

Fifty-four patients undergoing allogeneic HCT and 217 patients undergoing autologous HCT were included in the study cohort. Of the 54 allogeneic HCT patients, there were 35 (64.8%) allogeneic HCT patients in the intervention group that were compared to 19 (35.2%) allogeneic HCT patients in the historical control group. Although not significantly different, the intervention group tended to be slightly older at transplant (61 vs 51 median age, p = 0.0853) and included a smaller proportion of female patients (28.6% vs 52.6%, p = 0.0804). There were also no significant differences between the two groups of allogeneic HCT patients with regard to other baseline demographics such as race, ethnicity, disease, and conditioning (Table 1).

Table 1

Baseline allogeneic HCT patient characteristics.

	Intervention Group	Historical Control Group	All Patients
	N = 35 (64.8%)	N = 19 (35.2%)	N = 54 (100%)	P-Value
Age at Transplant, median (IQR)*	61 (50–64)	51 (35–59)	56 (46–63)	0.0853
Gender, female, no. (%)**	10 (28.6%)	10 (52.6%)	20 (37%)	0.0804
Race, no. (%)
Black/African American	2 (5.7%)	4 (21.1%)	6 (11.1%)	0.2693
Other/Unknown	2 (5.7%)	0 (0%)	2 (3.7%)
White	31 (88.6%)	15 (78.9%)	46 (85.2%)
Ethnicity, no. (%)
Hispanic or Latino	1 (2.9%)	1 (5.3%)	2 (3.7%)	1.0000
Not Hispanic or Latino	33 (94.3%)	18 (94.7%)	51 (94.4%)
Unknown	1 (2.9%)	0 (0%)	1 (1.9%)
Disease, no. (%)
Acute Leukemia	13 (37.1%)	8 (42.1%)	21 (38.9%)	0.4396
Lymphoma	4 (11.4%)	4 (21.1%)	8 (14.8%)
MDS/MPN	14 (40%)	4 (21.1%)	18 (33.3%)
Multiple Myeloma	1 (2.9%)	2 (10.5%)	3 (5.6%)
Other	3 (8.6%)	1 (5.3%)	4 (7.4%)
Myeloablative Conditioning, no. (%)	23 (65.7%)	13 (68.4%)	36 (66.7%)	0.8403

*t-test was used to test age difference and Wilcoxon Rank Sum tests were used for other continuous variables.

**Chi-squared test was used to test gender difference and Fisher’s exact tests were used for other categorical variables.

Of the 217 autologous HCT patients, there were 142 (65.3%) autologous HCT in the contemporaneous control group that were compared to 75 (34.7%) autologous HCT patients in the historical control group. The majority of patients in both groups received autologous HCT to treat multiple myeloma. There were no significant differences between the two groups of autologous HCT patients with regard to baseline demographics such as age at transplant, gender, race, ethnicity, and disease (Table 2).

Table 2

Baseline autologous HCT patient characteristics.

	Contemporaneous Control Group	Historical Control Group	All Patients
	N = 142 (65.3%)	N = 75 (34.7%)	217 (100%)	P-Value
Age at Transplant, median (IQR)*	60 (53–67)	62 (53–67)	61 (53–67)	0.6255
Gender, female, no. (%)**	55 (38.7%)	35 (46.7%)	90 (41.5%)	0.2592
Race, no. (%)
Black/African American	31 (21.8%)	19 (25.3%)	50 (23%)	0.6697
Other/Unknown	7 (4.9%)	5 (6.7%)	12 (5.5%)
White	104 (73.2%)	51 (68%)	155 (71.4%)
Ethnicity, no. (%)
Hispanic or Latino	3 (2.1%)	2 (2.7%)	5 (2.3%)	0.2176
Not Hispanic or Latino	138 (97.2%)	70 (93.3%)	208 (95.9%)
Unknown	1 (0.7%)	3 (4%)	4 (1.8%)
Disease, no. (%)
Acute Leukemia	1 (0.7%)	0 (0%)	1 (0.5%)	0.9319
Lymphoma	39 (27.5%)	18 (24%)	57 (26.3%)
Multiple Myeloma	96 (67.6%)	54 (72%)	150 (69.1%)
Other	6 (4.2%)	3 (4%)	9 (4.1%)

*t-test was used to test age difference and Wilcoxon Rank Sum tests were used for other continuous variables.

**Chi-squared test was used to test gender difference and Fisher’s exact tests were used for other categorical variables.

The allogeneic HCT patients in the intervention group displayed better compliance to stool collection protocols than the allogeneic HCT patients in the historical control group (Table 3). For instance, the mean overall collection rate in the intervention group of allogeneic HCT patients was much higher than the mean overall collection rate of the allogeneic HCT patients in the historical control group (80% vs 37%, p<0.0001). In addition to an increased mean overall collection rate, the allogeneic HCT patients in the intervention group also demonstrated significantly increased mean outpatient collection rates (84% vs 23%, p<0.0001) and significantly increased mean inpatient collection rates (71% vs 46%, p = 0.0409).

Table 3

Allogeneic HCT patient stool collection rates.

	Intervention Group	Historical Control Group	All Patients
	N = 35 (64.8%)	N = 19 (35.2%)	N = 54 (100%)	P-Value
Overall Collection Rate
Median (IQR)	0.875 (0.75–1)	0.375 (0–0.67)	0.75 (0.375–0.875)	< .0001
Mean (SD)	0.80 (0.24)	0.37 (0.36)	0.65 (0.35)
Outpatient Collection Rate
Median (IQR)	1 (0.8–1)	0 (0–0.5)	0.82 (0.25–1)	< .0001
Mean (SD)	0.84 (0.27)	0.23 (0.33)	0.64 (0.41)
Inpatient Collection Rate
Median (IQR)	0.8 (0.5–1)	0.5 (0–0.75)	0.75 (0.4–1)	0.0409
Mean (SD)	0.71 (0.36)	0.46 (0.41)	0.62 (0.40)

*Wilcoxon Rank Sum tests were used to test the rate differences.

On the other hand, there were no differences in compliance to stool collection protocols between the autologous patients in the contemporaneous control and historical control groups (Table 4). Mean overall collection rates were similar in both groups of autologous patients (36% vs 32%, p = 0.2760). Furthermore, mean outpatient collection rates (30% vs 28%, p = 0.5360) and mean inpatient collection rates (46% vs 59%, p = 0.2509) were comparable as well. Fig 2A demonstrates the proportion of stool samples collected at each time point in the outpatient setting, whereas Fig 2B demonstrates the proportion of stool samples collected in the inpatient setting, amongst the allogeneic and autologous transplant patients in the intervention and control groups.

Table 4

Autologous HCT patient stool collection rates.

	Contemporaneous Control Group	Historical Control Group	All Patients
	N = 142 (65.3%)	N = 75 (34.7%)	217 (100%)	P-Value
Overall Collection Rate
Median (IQR)	0.25 (0–0.75)	0.25 (0–0.5)	0.25 (0–0.67)	0.2760
Mean(SD)	0.36 (0.35)	0.32 (0.37)	0.35 (0.36)
Outpatient Collection Rate
Median (IQR)	0 (0–0.67)	0 (0–0.5)	0 (0–0.67)	0.5360
Mean(SD)	0.30 (0.36)	0.28 (0.38)	0.29 (0.37)
Inpatient Collection Rate
Median (IQR)	0.5 (0–1)	1 (0–1)	0.5 (0–1)	0.2509
Mean(SD)	0.46 (0.47)	0.59 (0.50)	0.49 (0.47)

Fig 2

(a) Outpatient Collections across Time Points for All Groups. Each collection time point is indicated at the top of the figure: Pre, T+0 (Day 0), T+ 1wk (Day 7), T+ 2wk (Day 14), T+ 3wk (Day 21), T+ 30d (Day 30), T+ 60d (Day 60), T+ 90d (Day 90). At each time point, the proportion of samples collected/not collected are shown for each group. If denoted as ‘collected’ (represented in black), this proportion of samples was successfully provided. If denoted as ‘not collected’ (represented in dark gray), this proportion of samples was not provided. If denoted as ‘NA’ (represented in light gray), this time point was not a required collection time point for that particular group. (b) Inpatient Collections across Time Points for All Groups. Each collection time point is indicated at the top of the figure: Pre, T+0 (Day 0), T+ 1wk (Day 7), T+ 2wk (Day 14), T+ 3wk (Day 21), T+ 30d (Day 30), T+ 60d (Day 60), T+ 90d (Day 90). At each time point, the proportion of samples collected/not collected are shown for each group. If denoted as ‘collected’ (represented in black), this proportion of samples was successfully provided. If denoted as ‘not collected’ (represented in dark gray), this proportion of samples was not provided. If denoted as ‘NA’ (represented in light gray), this time point was not a required collection time point for that particular group or, in the case of the day 90 time point, none of the samples were provided in the inpatient setting at this time point.

Table 5 displays a multivariate analysis modeling sample collection rates amongst the allogeneic transplant patients. The stool sample collection rate was 3.853 times higher in the intervention group than the stool sample collection rate in the historical control group (95% CI: 1.938, 7.657). There were no overall significant differences in sample collection rates after adjusting for covariates such as age, gender, conditioning, race, and disease. However, allogeneic transplant patients with lymphoma, MDS/MPN, or multiple myeloma, had significantly higher incidence rate ratios for sample collection rates when compared to allogeneic transplant patients with acute leukemia. Furthermore, African American allogeneic transplant patients had 2.658 times higher stool sample collection rates when compared to white allogeneic transplant patients (95% CI: 1.36, 5.194).

Table 5

Negative binomial regression with GEE on stool sample collection rate of allogeneic transplant patients.

	Incident Rate Ratio (95% CI)	P-Value	Overall P-Value
Group
Historical Control Group	-REF-		0.001
Intervention Group	3.853 (1.938–7.657)	<0.001
Age
Continuous	0.987 (0.971–1.003)	0.112
Gender
Male	-REF-		0.365
Female	0.756 (0.431–1.328)	0.331
Conditioning
Myeloablative	-REF-		0.140
NMA/RIC	0.603 (0.321–1.132)	0.115
Race
White	-REF-		0.098
Black/African American	2.658 (1.36–5.194)	0.004
Other/Unknown	0.967 (0.398–2.35)	0.942
Disease
Acute Leukemia	-REF-		0.068
Lymphoma	2.345 (0.938–5.863)	0.068
MDS/MPN	1.84 (1.039–3.258)	0.036
Multiple Myeloma	5.146 (1.993–13.287)	<0.001
Other	0.625 (0.183–2.134)	0.454

Discussion

With a significant increase in overall, outpatient, and inpatient collection rates in the intervention group, our results indicate that even moderate incentivization in the form of a $10 gas gift card can be efficacious in improving stool collection compliance in research. While this stands in contrast to other studies of $5-$20 incentives that showed no increase in collection rates of at-home fecal immunochemical testing or fecal occult blood testing, we believe our study demonstrates that a modest financial incentive of $10 for each stool sample is effective in procuring higher rates of stool samples for a couple of possible reasons [17-19]. For instance, the serial collection design of the study, requiring stool samples at multiple time points. The multiple time points provide a study participant in the intervention group multiple opportunities to earn a $10 gas gift card for each stool sample, thus the potential to actually earn more than $10 in gas gift cards during the entirety of the study. Another possible contributing factor for the effectiveness of financial incentives in our study was that study participants had the opportunity to return their required stool samples in-person at their clinic appointments, avoiding having to mail the sample which may be perceived by some as an additional inconvenience. Furthermore, employing a contemporaneous control group that did not receive the financial incentive into the study design addresses the possible confounders associated with potential discrepancies in stool collection rates over time, strengthening our finding that the increase in collection rates can be attributed to the financial incentive.

Despite the effectiveness of the financial incentive, our study is not without limitations. For instance, although accounted for in the statistical analyses, there are considerable differences in sample size between not only the comparison groups within each transplant type, but also between the total number of allogeneic and autologous transplant patients included in the study. The difference in the number of allogeneic and autologous transplant study participants is reflective of our patient population: about twice as many adult autologous stem cell transplants are performed each year than adult allogeneic transplants at Duke. Another limitation of the study is that the financial incentive was only made available to allogeneic transplant patients due to funding restraints; this was accounted for by only performing comparisons within the same transplant type. The non-randomization of the study is also a limiting factor because it does not take into account confounders such as social determinants of health that may make someone more or less inclined to participate in a research study involving financial incentives. Furthermore, although it was found that African American allogeneic transplant patients had higher stool sample collection rates when compared to white allogeneic transplant patients, there is a lack of racial and ethnic diversity in this study with the majority of study participants being non-Hispanic whites.

Effort on behalf of the patient is required most when providing a stool sample in the outpatient setting since patients must do the collection process themselves, as opposed to the inpatient setting where nursing staff aid with stool collection for admitted patients. Thus, the formidable boost in collection rates in the outpatient setting in the intervention group underscore the role of the financial incentive in this study. While the increase in inpatient collection rates in the intervention group is still significant, the average inpatient collection rate associated with the intervention group is mediated in the part by the role of nurses who work with patients to collect samples in that setting. Also, inpatient collection time points may have been missed when patients were only admitted for 24–48 hours for indications such as febrile neutropenia before being discharged to continue antibiotics in the outpatient setting, thus leaving a very narrow window for inpatient collection.

Furthermore, when utilizing financial incentives to motivate desired behaviors from patients, it is imperative to ensure the use of the financial incentive is ethical. For example, Bartholomew et al. raised concerns over the use of financial incentives in breast cancer screening, stating they may stimulate patients to make decisions they would not otherwise make, which can subsequently lead to patient harm (e.g. unnecessary treatment) [20]. However, the use of financial incentives in the context of our study is quite different. A participant’s decision to provide stool does not affect their treatment plan nor do they receive any sequencing results from their stool samples. The samples are not used for any sort of screening and have no effect on participant health; the stool samples are solely used for research purposes in order to improve outcomes of future patients. Undue inducement is another ethical concern that arises with financial compensation to research participants [21]. However, we believe the amount of $10 per stool sample was modest enough to not unduly influence a patient’s decision to participate in the study while still serving as an effective incentive to improve patient compliance to stool collection protocols.

While this study was performed in a specialized HCT patient population, this study design utilizing financial incentives to increase stool collection rates may be able to be executed in a myriad of patient populations. If these results are generalizable, other researchers attempting to procure stool samples for microbiome studies may be able to increase their patient compliance and improve their stool collection rates. Future directions for this study will be to observe the use of financial incentives for stool collection in the HCT population longitudinally in order to evaluate whether the effectiveness of the financial incentive would wear off over time. Furthermore, with more funding, autologous HCT patients can be included in the study. Another next step is to investigate how social determinants of health affect stool collection rates in the HCT population, identifying how factors such as socioeconomic status influence compliance and willingness to participate in a study utilizing financial incentives.

(XLSX)

Click here for additional data file.

(XLSX)

Click here for additional data file.

15 Feb 2022

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Peter Gyarmati

Academic Editor

PLOS ONE

Journal Requirements:

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

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at

https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

2. Thank you for stating the following in the Competing Interest section:

"I have read the journal's policy and the authors of this manuscript have the following competing interests:

MRM receives funding from Seres, Evelo, Jazz Pharmaceuticals, Therakos, Amgen, Merck & Co, Inc, Magenta Therapeutics, Smart Immune, Juno, and serves on the DKMS Advisory Board. ADS receives funding from Novartis, Merck, Seres, and serves as a consultant to AVROBIO. There is no overlap between ADS’ work with Novartis, Merck, AVROBIO, and this project. While Seres did fund the collection of stool samples, which led to some of the data presented, they had no role in data analysis and interpretation. Other than the competing interests statement, none of these companies will be mentioned by name."

We note that you received funding from a commercial source: Seres, Evelo, Jazz Pharmaceuticals, Therakos, Amgen, Merck & Co, Inc, Magenta Therapeutics, Smart Immune, Juno,Novartis, Merck and Seres.

Please provide an amended Competing Interests Statement that explicitly states this commercial funder, along with any other relevant declarations relating to employment, consultancy, patents, products in development, marketed products, etc.

Within this Competing Interests Statement, please confirm that this does not alter your adherence to all PLOS ONE policies on sharing data and materials by including the following statement: "This does not alter our adherence to PLOS ONE policies on sharing data and materials.” (as detailed online in our guide for authors http://journals.plos.org/plosone/s/competing-interests).  If there are restrictions on sharing of data and/or materials, please state these. Please note that we cannot proceed with consideration of your article until this information has been declared.

Please include your amended Competing Interests Statement within your cover letter. We will change the online submission form on your behalf.

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. 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: No

Reviewer #2: Yes

**********

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

Reviewer #1: No

Reviewer #2: Yes

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. 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 undertook a controlled before after study to measure the effect of a $10 petrol gift card on the collection of stool samples for patients undergoing allogenic hematopoietic stem cell transplantation. I have some concerns about the research reported here, both technical and ethical.

please see the file attached for detailed comments.

Reviewer #2: This timely article addresses a very hot and important topic of compensation in human microbiome research. The authors performed a prospective study on the impact of financial incentives on stool collections rates among stem cell transplantation patients and demonstrated that a modest incentive of 10 dollars can significantly increase collection rates. This results may inform the design of future studies involving stool collection, given the rapid development of human microbiome research, the value of study is obvious. However, there are still some weaknesses of this paper.

Firstly, the author may need to explain why $10？what's the normal compensation amount in clinical trials setting in their country?

Secondly, the authors may need to consider the appropriateness of the compensation type regarding the participant population, what about other types of compensation?

Thirdly, Financial compensation is closely related with undue inducement, which refers to compensation that is so great in amount or nature that it decreases participants' ability to rationally consider participation in the study. The compensation should not be so large that individuals may feel compelled to participate. The authors are suggested to include a discussion on how to avoid undue inducement while incentivise participation and stool collection compliance in research.

Fourthly, is there any particular vulnerabilities with the patient group the paper focused? would their vulnerabilities affect their participation in fecal collection?

If authors want to get back to the work by addressing these issues, this would make for a far more targeted and clearer discussion.

**********

6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: Yes: Isabelle Durand-Zaleski

Reviewer #2: Yes: Yonghui Ma

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

Submitted filename: financial incentives_PLOSONE_Jan2022.docx

Click here for additional data file.

Submitted filename: PONE-D-21-40817+comments.pdf

Click here for additional data file.

31 Mar 2022

Response to Reviewers

Thank you very much for consideration of our manuscript, and we greatly appreciate your feedback and commitment to the peer review process. Please see a point-by-point response to the reviewers’ comments. We have revised the paper accordingly.

Reviewer #1: The authors undertook a controlled before after study to measure the effect of a $10 petrol gift card on the collection of stool samples for patients undergoing allogenic hematopoietic stem cell transplantation. I have some concerns about the research reported here, both technical and ethical.

please see the file attached for detailed comments.

The topic of financial incentives for patients is debated on grounds of both efficacy and ethics. A checklist was developed for healthcare professionals (Glasziou PP, Buchan H, Del Mar C, Doust J, Harris M, Knight R, Scott A, Scott IA, Stockwell A. When financial incentives do more good than harm: a checklist. BMJ. 2012 Aug 13;345:e5047. doi: 10.1136/bmj.e5047. PMID: 22893568.) and some of the items can also be relevant for financial incentives directed to patients:

Thank you for suggesting this helpful framework for assessing the appropriateness of a financial incentive. After thorough consideration of the checklist, we believe that the financial incentive utilized in our study is appropriate, as we can answer ‘yes’ to the aforementioned questions. Please see below for responses to the specific questions:

1. Does the desired action improve patient outcomes?

Response: Yes, we believe the desired action of obtaining stool samples from patients undergoing hematopoietic stem cell transplantation (HCT) will improve patient outcomes by providing invaluable information about the role of the microbiome in HCT patients, as discussed in the introduction of our manuscript. In addition to the introduction of our manuscript, a recently published paper by some of our co-authors in The New England Journal of Medicine further emphasized the pertinence of learning more about the microbiome of HCT patients by demonstrating that lower mortality was associated with increased diversity of intestinal microbiota at the time of engraftment in patients undergoing allogeneic HCT, an association gleaned from the analysis of many stool samples (van den Brink MD et al. Microbiota as Predictor of Mortality in Allogeneic Hematopoietic-Cell Transplantation. N Engl J Med. 2020 Feb 27; 382:822-834. doi: 10.1056/NEJMoa1900623. PMID: 32101664). Learning more about the microbiome in HCT patients, and most importantly learning more about how to utilize this data to decrease morbidity and mortality, necessitates collecting stool from these patients.

2. Will undesirable behaviour persist without intervention?

Response: Yes, we believe that undesirable behavior (patient noncompliance with stool collection protocols) will persists without intervention (modest, noncoercive financial incentive), as demonstrated by the results of our manuscript. For instance, allogeneic HCT patients in the intervention group had significantly higher average overall collection rates when compared to the historical control group allogeneic HCT patients (80% vs 37%, p<0.0001). Collection rates were also low in the autologous HCT patients in the contemporaneous control and historical control groups who were not compensated with no significant difference in the collection rates between these groups of autologous patients (36% vs 32%, p=0.2760). In addition to the results of our manuscript, other studies also demonstrated difficulty in trying to obtain stool samples from patients (please see introduction of this manuscript for specific studies, line 77-90). Thus, we believe that poor stool sample collection rates will persist without the utilization of modest financial incentives.

3. Are there valid, reliable, and practical measures of the desired behaviour?

Response: Yes, there are valid, reliable, and practical measures of stool collection. Assessing stool collection through collection rate, defined as the number of samples provided divided by the number of time points we attempted to obtain stool, is an objective way to measure participant compliance to providing stool samples. We also believe that assessing stool collection this way is reliable (precise and reproducible) and will be able to be reproduced by other teams attempting to collect stool for microbiome studies.

4. Have the barriers and enablers to improving behaviour been assessed?

Response: Yes, the barriers and enablers to improving patient compliance with providing stool samples was assessed through literature review. Please see introduction of manuscript (lines 77-90).

5. Will financial incentives work, and better than other interventions to change behaviour, and why?

Response: Yes, we believe that financial incentives will work in improving patient compliance in providing stool samples, based on the results of our studies and others mentioned in the introduction of the manuscript. We also believe that financial incentives work better than other interventions based on the stool collection rates of the control groups. For example, all patients, regardless of group, receive education on how to provide stool by the study coordinator during the consent process, as well as reminders to bring their stool samples with them at required time points. While not specifically assessed, the low compliance in the groups who were not compensated demonstrate that other methods to improving compliance such as patient education and reminders are not enough to significantly improve stool collection rates. This was not specifically assessed, but can be inferred by the results of the study.

6. Will benefits clearly outweigh any unintended harmful effects, and at an acceptable cost?

Response: Yes, the benefits to collecting stool (please see response to question 1) outweigh any unintended harmful effects. Furthermore, our IRB-approved protocols (Pro00006268, Pro000078566) lists no “Expected Adverse Events” for stool collection: ‘

Stool Collection: There are no known risks associated with the collection of stool samples. There may be risks, discomforts, or side effects that are not yet known.”

Also, providing stool as part of the study does not affect the patient-clinician relationship since a study coordinator not involved in the direct care of the patient handles consenting and other study-related tasks.

The authors undertook a controlled before after study to measure the effect of a $10 petrol gift card on the collection of stool samples for patients undergoing allogenic hematopoietic stem cell transplantation. I have some concerns about the research reported here, both technical and ethical.

General comments

I think a discussion on the appropriateness and ethics of the financial incentive in this context, based for example on the BMJ checklist and on the following article (Bartholomew T, Colleoni M, Schmidt H. Financial incentives for breast cancer screening undermine informed choice. BMJ. 2022 Jan 10;376:e065726. doi: 10.1136/bmj-2021-065726. PMID: 35012959.), would be welcome. Also I would question the opportunity of gift cards for petrol at a time when we are globally trying to reduce pollution. Why the choice of petrol and not vouchers for cultural goods as in BMJ 2021;375:e065217 for example?

Response: Thank you for this recommendation. Bartholomew et al. make some excellent points in regards to the role of financial incentives in breast cancer screening. However, we feel that the use of financial incentives to increase stool collection in the context of our study is quite different for the following reasons. For example, unlike breast cancer screening that may lead to psychological distress from false positives or unnecessary treatment as mentioned in the article, participants providing stool samples in the context of our study does not affect their treatment plan nor do they receive any sequencing results from their stool samples. The samples are not used for any sort of screening and have no effect on participant health. The process of providing stool is noninvasive, and there are no known risks associated with the collection of stool samples. The stool samples are solely used for research purposes in order to learn more about how to use the microbiome to improve outcomes of future patients. Furthermore, unlike the process of consenting for breast cancer screening by physicians attempting to make screening quotas, there is no undue influence driven by conflicts of interest during the consenting process for our study since a study coordinator who is not a part of the healthcare team does the consenting. Finally, the Bartholomew et al. article mentions that “the fundamental ethical concern with incentives is that they may lead people to make choices they would not have made without the incentive are harmed by this choice.” There is no known harm involved in providing a stool sample since it has no influence on patient care as described above, and we used an IRB-approved study protocol that deemed $10 modest enough to not have undue influence on patient decision making. The consent forms were also part of this IRB approved study and were thoroughly explained to patients by study coordinators with a sole focus of promoting patient autonomy and well-being. Thus, we believe the use of financial incentives in our study to be ethical.

Please also note the stool and blood samples are collected based on our standing IRB approved biorepository protocols (Pro00006268, Pro000078566). Participation is voluntarily and will not affect the treatment as required by the IRB. The stool collection protocol was not stablished around the $10 incentives.

In regards to the decision to use petrol gift cards as the incentive, we agree that it is very important to be environmentally conscious; however, many of our patients are driving very long distances to reach their appointments at the Duke Adult Bone Marrow Transplant Clinic. The majority of our patients are not local patients. They might have been driving from rural areas of NC or even other states. These patients have no other option but to use gas in order to get to their appointments. Thus, gas gift cards for $10 was an option that we felt would be an effective incentive without too much value to be considered coercive.

Furthermore, due to the nature of the disease, difficult treatment and post HCT periods of time, other vouchers might not be appropriate or useful to our patient population. The mortality and morbidity rate of HCT post treatment can be as high as 30%, these are venerable and immune suppressed patient population. Even without a global pandemic, many of the cultural events or social settings won’t be appropriate in this setting.

Hopefully by 2030-2035 (EU and US), when the goal is to have most of the cars independent of gas, our patients have the option not to drive traditional cars. Thus, help with environmental protection. As of now electric cars are out of reach of majority of the world population for many reasons including cost.

Do patients derive a personal benefit from the microbiome study, in terms of treatment adaptation for example, or is it only for research that will eventually benefit other patients later?

Response: That’s a great question. No, patients do not derive a personal benefit from the microbiome study. These samples are just used for research that is aimed to benefit future patients.

For the primary endpoint, I would like an explanation of how it was calculated. What does a mean rate of 80% mean in Table 3, is it 80% of the population who brought the planned 8 stools? Or is it the total number of stools divided by 8 and by the total population? What is the most important for you research, to have the required number of samples for the population of to have as many patients as possible with at least one stool?

Response: It means the average of all the patients’ collection rates. Collection rate is defined as the number of submitted samples divided by the number of required or maximum possible number of submissions. Collection rate is more important for our research, as opposed to as many patients as possible with at least one stool, in order to assess the changes to the microbiome over time as a patient goes through the HCT process. In addition to that, our objective was trying to get more samples from one patient, instead of just one sample from one patient.

Specific comments:

Why is collection rate, and not the total number of stools collected chosen as the endpoint?

Response: Please see answer to previous question above. Furthermore, the allogeneic and autologous transplant patients have different sample collection timelines since allogeneic patients have to come to the clinic more frequently after transplant due to the more rigorous post-transplant recovery. Thus, we attempted to collect stool samples from the allogeneic patients at the following time points: pre-HCT, Day 0, Day 7, Day 14, Day 21, Day 30, Day 60, and Day 90. On the other hand, stool samples were only collected from autologous patients at pre-HCT, Day 7, Day 14, and Day 90. Plus, if a participant withdrew from the study or died, then the subsequent time points after date or death or withdrawal were not included in the analysis. Thus, the maximum number of possible samples collected from each patient can be different.

Also I am not sure that the term ‘rate’ is mathematically correct if you mean percentage. Is time a variable included in your rate calculations?

Response: Time is not a variable included in the rate calculations. In this context, we believe ‘rate’ is the correct calculation as it presents a frequency of discrete submissions.

I understood from Fig 1 that 8 samples are planned. Why not report the average number of stools collected per patient and per period (before/after)?

Response: We intended for Figure 1 to represent an overview of the sample collection timeline for the different groups. Stool samples were planned to be collected from allogeneic HCT patients at 8 different time points whereas samples were planned to be collected from autologous HCT patients at 4 different time points. The group of historical control allogeneic patients consists of different patients than the intervention allogeneic patients. That is why we didn’t compare before and after. The historical control autologous group consist of different patients than the contemporaneous control autologous group. Please see “Defining groups and sample collection” of the Materials and methods section.

Why is the total number of stools collected not reported in the auto group either? I saw that all the figures are I the excel file so it would be possible to present at least the endpoints that I think would be relevant:

- % of patients with a full stool collection before/ after and in the control group.

- % of the total number of samples collected (N collected / N population x8)

Response: We chose not to report the absolute number since the collection rate better portrays compliance to stool collection protocol since the allogeneic and autologous patients have different sample collection schedule and to account for patient death and dropout. Please see above.

Why is there no sample size calculation?

Response: A priori sample size calculation was not performed for this study. While this study was approved by the Duke IRB and written informed consent was obtained from all study participants, this study was not formally planned. However, all statistical analyses were performed appropriately, and the limitations related to the sample size in our study have been addressed in the discussion (please see lines 292-297 in our manuscript).

The bar graphs figure 2 a and 2b are very difficult to read, I would suggest a figure like this, with line and an arrow indicating the introduction of the incentive in the alloHCT intervention group (https://qualitysafety.bmj.com/content/25/5/303)

Response: Thank you for this suggestion. There are only two effective timepoints for allos and two for autos, which there are three timepoints in sequence, but it is not appropriate to make one line connecting the different groups of patients. We believe this format will require many lines to present the same information as one bar plot can present since there are 4-8 time points for each patient depending on their group.

Reviewer #2: This timely article addresses a very hot and important topic of compensation in human microbiome research. The authors performed a prospective study on the impact of financial incentives on stool collections rates among stem cell transplantation patients and demonstrated that a modest incentive of 10 dollars can significantly increase collection rates. This results may inform the design of future studies involving stool collection, given the rapid development of human microbiome research, the value of study is obvious. However, there are still some weaknesses of this paper.

Firstly, the author may need to explain why $10？what's the normal compensation amount in clinical trials setting in their country?

Response: Thank you for this question. We chose $10 because we believed that this amount was modest enough to not unduly influence a patient’s decision to participate in the study (i.e. not excessive enough to be persuasive or coercive) while still serving as an effective incentive to improve patient compliance to stool collection protocols. Furthermore, this modest amount may help other study teams to reproduce this process for their own studies who may have limited resources while still leading to increased collection rates. While it was difficult to find a specific range for the normal compensation amount in the clinical trial setting in the United States , a study from one stool bank paid $40 for stool samples (Chen J, Zaman A, Ramakrishna B, Olesen S. Stool banking for fecal microbiota transplantation: methods and operations at a large stool bank. Frontiers. 2021 April 15; doi: 10.3389/fcimb.2021.622949). Some other studies (cited in the discussion of our manuscript) utilized $5-$20 incentives to try to increase patient compliance.

Secondly, the authors may need to consider the appropriateness of the compensation type regarding the participant population, what about other types of compensation?

Response: We believe that the $10 gas gift card was an appropriate form of compensation for this patient population that consisted of many patients who had to drive very long distances to reach their appointments at the Duke Adult Bone Marrow Transplant Clinic. Thus, we felt that the $10 gas gift card would be an effective incentive without being of too much value to be considered unduly influential. Please also see our response above to reviewer 1’s general comment.

Thirdly, Financial compensation is closely related with undue inducement, which refers to compensation that is so great in amount or nature that it decreases participants' ability to rationally consider participation in the study. The compensation should not be so large that individuals may feel compelled to participate. The authors are suggested to include a discussion on how to avoid undue inducement while incentivise participation and stool collection compliance in research.

Response: Thank you for this suggestion. You bring up a great point, and we agree that research should always be conducted in a manner that promotes the utmost respect for participants and encourages full participant autonomy during the informed consent process. In order to avoid undue inducement while still incentivizing participation and compliance in stool collection research, it is important to choose an amount of compensation that is considered modest enough to not hinder appropriate participant judgment during informed decision making while also ensuring adequate compensation for such a task that is considered quite repulsive by most (i.e. collecting one’s own stool). In order to do this, the amount of compensation should be chosen ahead of time as part of a protocol that is approved by the institutional review board before starting any study related activities. Furthermore, ensuring good research practices by having a study coordinator who is not part of the direct care team carry out a thorough consenting process (e.g. explaining all risks and benefits, emphasizing the decision to participate is completely voluntary, etc.) can help participants to rationally consider participation in the study.

Fourthly, is there any particular vulnerabilities with the patient group the paper focused? would their vulnerabilities affect their participation in fecal collection?

If authors want to get back to the work by addressing these issues, this would make for a far more targeted and clearer discussion.

Response: This is always something very important to consider. There were no particular vulnerabilities with the participants in our study. Please see below for an excerpt about vulnerable populations from our IRB approved protocol of the study:

“As this study is built around the Duke Adult Bone Marrow Transplant Program, which only treats patients age 18 and older, fetuses, neonates, and children will be excluded. While subjects may be as old as 80 years, adults with cognitive impairment and unable to consent to participation will not be enrolled. Pregnant women are excluded from transplant and will therefore be excluded from this study. Prisoners and institutionalized individuals are also excluded from this study.”

Furthermore, a next step of this project is to investigate how social determinants of health affect stool collection rates in the HCT population in order to see if factors such as socioeconomic status influence compliance and willingness to participate.

*Copied from PDF comment and already addressed above

the authors may need to consider the appropriateness of the compensation type regarding the participant population, what about other types of compensation?

Response: Please see above, thank you.

Financial compensation is closely related with undue inducement, which refers to compensation that is so great in amount or nature that it decreases participants' ability to rationally consider participation in the study. The compensation should not be so large that individuals may feel compelled to participate. The authors are suggested to include a discussion on how to avoid undue inducement while incentivise participation and stool collection compliance in research.

Response: Please see above, thank you.

the author may need to explain why $10? and what's the average compensation amount for encouraging compliance in clinical trials in their country? for example, in China, the compensation for each visit in clinical trials setting is between 100-200RMB.

Response: Please see above, thank you.

Submitted filename: Response to Reviewers-03-30-22.docx

Click here for additional data file.

13 Apr 2022

14 Apr 2022

Rebuttal letter: Thank you very much for consideration of our manuscript, and we greatly appreciate your feedback and commitment to the peer review process. Please see our response to the reviewers’ comments. We have revised the paper accordingly.

04-14-2022

PONE-D-21-40817R1

Financial incentives to increase stool collection rates for microbiome studies in adult bone marrow transplant patients

PLOS ONE

Please include the following items when submitting your revised manuscript:

• A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

Response: the rebuttal letter has been uploaded.

• A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

Response: 'Revised Manuscript with Track Changes' has been uploaded.

• An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

Response: Manuscript has been uploaded.

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: 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: Partly

Reviewer #2: Yes

________________________________________

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

Reviewer #1: No

Reviewer #2: Yes

________________________________________

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

________________________________________

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

________________________________________

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: Please add in the statistical analysis section the sentence written in your answers to reviewers:

'A priori sample size calculation was not performed for this study. While this study was

approved by the Duke IRB and written informed consent was obtained from all study participants,

this study was not formally planned. '

Response: The requested information has been added to the statistical analysis of the methods section.

Reviewer #2: The author has addressed issues raised in the comments and greatly improved the quality and soundness of paper, therefore, I recommend the paper to be published.

Response: Thank you.

Submitted filename: Response to reviewers_Thompson04-14-22.docx

Click here for additional data file.

20 Apr 2022

Financial incentives to increase stool collection rates for microbiome studies in adult bone marrow transplant patients

PONE-D-21-40817R2

Dear Dr. Sung,

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.

An invoice for payment will follow shortly after the formal acceptance. To ensure an efficient process, please log into Editorial Manager at http://www.editorialmanager.com/pone/, click the 'Update My Information' link at the top of the page, and double check that your user information is up-to-date. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. 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.

Kind regards,

Peter Gyarmati

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

25 Apr 2022

PONE-D-21-40817R2

Financial incentives to increase stool collection rates for microbiome studies in adult bone marrow transplant patients

Dear Dr. Sung:

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. Peter Gyarmati

Academic Editor

PLOS ONE