Principal Findings
SECONDARY, EMA
This study experimentally evaluated the effect of rewards and schedule length on EMA response rates within the context of an ongoing study implementing repeated bursts of EMA surveys. Reducing the number of days of EMA surveys led to a significantly lower response rate. However, changing the available rewards did not significantly change the response rate. Overall, for all groups the response rate was lowest at baseline (burst 1) as compared with the subsequent bursts of EMAs and the difference was statistically significant. However, our subgroup analysis that was intended to further explore whether this was because of changes in how participants were notified of the relevant burst of EMA surveys found no significant difference in the response rate at each burst.The response rate to burst 1 was very low, prompting this study, and increased substantially in burst 2 and burst 3 in all groups. It is possible that the initial low response rate was because the upcoming EMA burst was not well communicated to the participants. Future bursts included more frequent communication delivered directly to all participants (via SMS text messages and push notifications). These simple changes may have contributed to the increased response rate. However, we did not experimentally evaluate the effects of these communication changes. Our secondary analysis partially supported this finding, as there were significant differences between the response rate at each burst. However, in the subgroup analysis of the control group participants, the differences were no longer significant.