Impact of different unconditional monetary incentives on survey response rates in men with prostate cancer: a 2-arm randomised trial

Background: Men are often viewed as a difficult group to recruit for psychological research, including in psycho-oncology. Whilst research has demonstrated the effectiveness of small monetary incentives for encouraging research participation, little research has examined different large unconditional incentive amounts. Larger unconditional incentives may result in increased participation of men in psychological research. This randomised study within a case–control trial of men diagnosed with early-stage prostate cancer aimed to investigate whether (a) response rates to a 30-min questionnaire completed via mail, online, or phone would vary with different unconditional incentive amounts, and (b) demographics would vary in those who responded within the different incentive groups. Methods: We conducted this randomised study within a case–control cross-sectional study aiming to identify the social-ecological factors influencing treatment discontinuation in prostate cancer patients. A total of 238 participants from the cross-sectional study were randomised to receive one of two unconditional incentives (n = 121 received AUD$10, n = 117 received AUD$20) with the study materials (consent form and survey). Results: Overall, 113 (47%) responded; n = 61/121 (50.4%) in the AUD$10 group, and n = 52/117 (44.4%) in the AUD$20 group. No evidence of a difference was found in response rates by incentive group (odds ratio 1.27, 95% CI = 0.76–2.12, p = 0.36). Additionally, there were no evident differences in the demographics of the responders vs. non-responders within each incentive group (all p > 0.05). Conclusions: Unlike previous research, we were unable to show that higher monetary incentives were more effective for increasing response rates. An AUD$20 unconditional incentive may be no more effective than a lesser amount for encouraging prostate cancer survivors to participate in research involving long questionnaires. Future research should consider the cost-benefits of providing large unconditional incentives, as non-responses will result in lost resources perhaps better utilised in other engagement strategies.