Objective To investigate the effect of monetary incentive and the dose–response relationship of participants’ response rates in surveys.
Methods Three databases were searched for randomised controlled trials (RCTs) that investigated the effect of monetary incentives on participants’ first and final response rates. First response is defined as the responses after the participant was initially contacted and final response is defined as the responses after several reminders were sent. The potential dose–response relationship of the amount of monetary incentive on the relative response rate (RRR) was established by fitting a restricted cubic spline function based on the robust-error meta-regression model.
Results 105 RCTs were identified. The first RRR increased by 49% (RRR=1.49; 95% CI 1.29 to 1.72) when monetary incentives were provided. Dose–response analysis revealed that an amount between US$6.25 and US$8 had the maximum effect on increasing the first response rate. On average, the final RRR increased almost by 20% (RRR=1.18; 95% CI 1.11 to 1.25) with monetary incentive compared to no-monetary incentive. An amount between US$10 and US$15 had the maximum effect on the final response rate, with an increase in the final RRR of 34% (RRR=1.34; 95% CI 1.19 to 1.51). There was a significant increase in the response rate when two or more reminders were sent.
Conclusion Monetary incentives and reminders improve the response rates. Future studies need to consider providing monetary incentives and sending at least two reminders to increase the response rate and reduce the chances of non-response bias.
- Infectious diseases
- Clinical trials
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Contributors CX and PJ conceived and designed the study; PJ, P-YJ and CX conducted the data collection; CX and LF-K analysed the data; PJ drafted the manuscript; LF-K, Z-SQ and P-YJ provided careful comments and revised the manuscript. All authors read and approved the manuscript.
Funding PJ was supported by the Science Research Start-up Fund for Doctor of Shanxi Province (SD1819). LF-K is funded by an Australian National Health and Medical Research Council Early Career Fellowship (APP1158469). The funding sources had no role in the design, data collection, analysis, interpretation of the data or decision to submit the results.
Competing interests None declared.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are available in a public, open access repository. The dataset supporting the conclusions of this article is included within the article and its supplementary materials.
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