Improving response rates using a monetary incentive for patient completion of questionnaires: an observational study

We recruited patients in general practice with knee problems from sites across the United Kingdom. An evidence-based strategy was used to follow-up patients at twelve months with postal questionnaires. This included an unconditional direct payment of ￡5 to patients for the completion and return of questionnaires. The first 105 patients did not receive the ￡5 incentive, but the subsequent 442 patients did. We used logistic regression to analyse the effect of introducing a monetary incentive to increase the response to postal questionnaires.The response rate following reminders for the historical controls was 78.1% (82 of 105) compared with 88.0% (389 of 442) for those patients who received the ￡5 payment (diff = 9.9%, 95% CI 2.3% to 19.1%). Direct payments significantly increased the odds of response (adjusted odds ratio = 2.2, 95% CI 1.2 to 4.0, P = 0.009) with only 12 of 442 patients declining the payment. The incentive did not save costs to the trial – the extra cost per additional respondent was almost ￡50.The direct payment of ￡5 significantly increased the completion of postal questionnaires at negligible increase in cost for an adequately powered study.The randomised trial is widely accepted as the most rigorous research method for minimising bias when evaluating health care technologies [1]. It is important to undertake randomised trials in primary care to produce an evidence base that is relevant to the health care delivered in that setting [2,3]. Recruitment of health care professionals and patients to randomised trials in primary care can be very difficult [4,5]. This also applies to the completion of postal questionnaires which are frequently used in trials when collecting data (including primary outcomes) from patients and practitioners [6]. Furthermore the completion of questionnaires is important for other study designs such as cohorts and surveys. These studies require informed consent but not to the same commitment as for a trial which in itself migh