Chocolate bar as an incentive did not increase response rate among physiotherapists: a randomised controlled trial

BACKGROUND: The aim of this study was to assess the effect of a small incentive, a bar of dark chocolate, on response rate in a study of physiotherapy performance in patients with knee osteoarthritis. FINDINGS: Norwegian physiotherapists from private practice were randomised in blocks to an intervention group (n = 1027) receiving a bar of dark chocolate together with a data-collection form, and a control group (n = 1027) that received the data-collection form only. The physiotherapists were asked to prospectively complete the data-collection form by reporting treatments provided to one patient with knee osteoarthritis through 12 treatment sessions. The outcome measure was response rate of completed forms. Out of the 510 physiotherapists that responded, 280 had completed the data-collection form by the end of the study period. There was no difference between the chocolate and no-chocolate group in response rate of those who sent in completed forms. In the chocolate group, 142 (13.8%) returned completed forms compared to 138 (13.4%) in the control group, ARR = 0.4 (95% CI: -3.44 to 2.6). CONCLUSION: A bar of dark chocolate did not increase response rate in a prospective study of physiotherapy performance. Stronger incentives than chocolate seem to be necessary to increase the response rate among professionals who are asked to report about their practice. TRIAL REGISTRATION: Current Controlled Trials register: ISRCTN02397855