Abstract
BackgroundSending a monetary incentive with postal questionnaires has been found to improve the proportion of responders, in research in non-healthcare settings. However, there is little research on use of incentives to improve follow-up rates in clinical trials, and existing studies are inconclusive. We conducted a randomised trial among participants in the Managing Injuries of the Neck Trial (MINT) to investigate the effects on the proportion of questionnaires returned and overall non-response of sending a £5 gift voucher with a follow-up questionnaire.MethodsParticipants in MINT were randomised to receive either: (a) a £5 gift voucher (incentive group) or (b) no gift voucher (no incentive group), with their 4 month or 8 month follow-up questionnaire. We recorded, for each group, the number of questionnaires returned, the number returned without any chasing from the study office, the overall number of non-responders (after all chasing efforts by the study office), and the costs of following up each group.Results2144 participants were randomised, 1070 to the incentive group and 1074 to the no incentive group. The proportion of questionnaires returned (RR 1.10 (95% CI 1.05, 1.16)) and the proportion returned without chasing (RR 1.14 (95% CI 1.05, 1.24) were higher in the incentive group, and the overall non-response rate was lower (RR 0.68 (95% CI 0.53, 0.87)). Adjustment for injury severity and hospital of recruitment to MINT made no difference to these results, and there were no differences in results between the 4-month and 8-month follow up questionnaires. Analysis of costs suggested a cost of £67.29 per additional questionnaire returned.ConclusionMonetary incentives may be an effective way to increase the proportion of postal questionnaires returned and minimise loss to follow-up in clinical trials.Trial registration numberISRCTN61305297
Highlights
Sending a monetary incentive with postal questionnaires has been found to improve the proportion of responders, in research in non-healthcare settings
A Cochrane systematic review of randomised trials of monetary incentives to promote questionnaire return showed that this intervention was effective.[1]
Dirmaier et al[3], in a study of patients being followed up after inpatient treatment for mental health problems, found a 7.3% increase with a small monetary incentive, and Kenyon et al[4] found an improvement of 11.7% with a £5 gift voucher, in a study of longterm follow-up of participants in a randomised trial of antibiotics for preterm labour[9,10]
Summary
Sending a monetary incentive with postal questionnaires has been found to improve the proportion of responders, in research in non-healthcare settings. Failure to return questionnaires results in missing data, which could potentially introduce bias into the trial's results, and strategies are frequently employed to promote questionnaire return Often this involves a system of follow-up contacts by post and telephone to ensure that data are collected from as many participants as possible. A Cochrane systematic review of randomised trials of monetary incentives to promote questionnaire return showed that this intervention was effective (OR 1.99, 95% CI 1.81, 2.18).[1] the majority of the studies in this review were not conducted in healthcare settings and none of them involved participants in clinical trials. There is uncertainty as to whether monetary incentives are effective, and further research is justified
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