Comparison of up-front cash cards and checks as incentives for participation in a clinician survey: a study within a trial

We surveyed the first 125 PCPs from each city who were elected by a BFOR participant to share his or her BRCA1/2 results. Using a combination of questions derived from other surveys [14‐16] and questions developed specifically for the BFOR project (Supplement), the survey gathered general demographic and practice information, assessment of BRCA1/2 mutation knowledge, PCPs’ opinions on incorporating genetic testing into their existing practices, and willingness to disclose the results of their patients’ testing obtained through the BFOR study. We mailed paper surveys, although we also provided PCPs the option to participate via the Internet. Each initial survey mailing included a personalized cover letter, an up-front, unconditional $50 incentive, a four-page survey designed to be completed in less than 10 min, and a pre-paid return envelope. Surveys were prelabeled with each PCP’s assigned study identification number to allow study staff to identify which PCPs had already responded; no other identifiers were included in PCPs’ responses. First and second reminders were sent via mail roughly three and 6 weeks, respectively, after the initial mailing. These reminders contained personalized letters, a second copy of the survey, and a pre-paid return envelope.

Whenever a patient requested that their PCP disclose their results, that PCP immediately became eligible for the survey study and was assigned by research staff to receive $50 cash card or $50 check incentive. (Fig. 1) Assignment was performed as follow: as PCPs were nominated by their patients, they were assigned a study ID based on their region. Within each region, we used an alternating 1:1 allocation strategy to assign newly enrolled PCPs to receive a cash card or check. The cash cards were reloadable debit cards that required activation by the study managers before use. PCPs received instructions accompanying the card informing them the if they wished to activate the cash card they had to email a study manager with their card number and request card activation. In June 2018, in an effort to increase response rates, we additionally decided to send out third reminders to PCPs. The third reminder included a personalized letter, third copy of the survey, pre-paid return envelope, and a second incentive equivalent to the first. In June 2018, in an effort to increase response rates, we additionally mailed third reminders to PCPs. The third reminder included a personalized letter, third copy of the survey, pre-paid return envelope, and a second incentive equivalent to the first. We planned to send third reminders to all PCPs who had not yet responded to the survey, but third reminders were subsequently discontinued due to study staffing limitations. The third reminders were sent to the first 42 nonresponding PCPs who had been assigned to receive cash cards (providing them with a second cash card); third reminders were also planned for nonresponding PCPs who had been assigned to receive checks. However, issuing checks took more time than issuing cash cards, and the third reminder initiative was terminated before any third-reminder letters with checks were actually mailed. Our target sample size for the PCP survey study was 500 (125 per region), based on a sample size calculation derived from anticipated differences in factors influencing PCPs’ willingness to disclose their patients’ BRCA1/2 results and a response rate of 50% derived from rates in other provider surveys [6, 17, 18]. After June 2018, due to overall response rates below 50% and early findings demonstrating that checks yielded higher response rates, the randomized study of incentives was stopped and all further survey mailings to newly enrolled PCPs included checks. This analysis includes the 303 PCPs enrolled in the randomized portion of the study between December 2017 and June 2018. Among these, 155 were assigned to receive their incentive in the form of a cash card and 148 were assigned to receive a check.

Our pre-specified primary outcome was response to the survey; staff determining this outcome were not blinded to the exposure. Our primary independent variable was receipt of a cash card versus check. Covariates were clinician city, specialty and sex; these were the demographic and practice data that were available for both responding and non-responding PCPs.

We used univariate Chi-square tests to examine response rates according to whether PCPs received checks or cash cards and according to PCP sex, city and specialty. Because more female PCPs were assigned to checks than males, we used multivariate logistic regression to adjust analyses for demographic characteristics. We also conducted stratified analyses of the impact of checks versus cash cards according to demographic characteristics, and we noted that the impact of checks versus cash cards appeared to vary by city. To explore this further, we incorporated interaction terms into our model. Finally, we conducted sensitivity analyses in which we reclassified as non-responding the 4 PCPs who had responded to the survey only after receiving a third survey reminder letter, since only a subset of PCPs received this third reminder. Statistical analyses were performed using SAS version 9.3 (Copyright 2002–2012, Cary, North Carolina).

This study adhered to the TREND checklist for reporting of nonrandomized studies (https://​www.​cdc.​gov/​trendstatement/​). The BFOR study protocol is registered on clinicaltrials.​gov (NCT03351803). The protocol for the survey incentives study described here was developed a priori subsequent to the overall BFOR study protocol and submitted to the institutional review board prior to participant enrollment.