Unconditional and conditional monetary incentives to increase response to mailed questionnaires: A randomized controlled study within a trial (SWAT)

Abstract

Rationale, aims, and objectives: High response rates to research questionnaires can help to ensure results are more representative of the population studied and provide increased statistical power, on which the study may have been predicated. Improving speed and quality of response can reduce costs. Method:We conducted a randomized study within a trial (SWAT) to assess questionnaire response rates, reminders sent, and data completeness with unconditional compared with conditional monetary incentives. Eligible individuals were mailed a series of psychological questionnaires as a follow-up to a baseline host trial questionnaire. Half received a £5 gift voucher with questionnaires (unconditional), and half were promised the voucher after returning questionnaires (conditional).Results: Of 1079 individuals, response rates to the first follow-up questionnaire were 94.2% and 91.7% in the unconditional and conditional monetary incentive groups, respectively (OR 1.78; 95% CI, 0.85-3.72). There were significantly greater odds of returning repeat questionnaires in the unconditional group at 6 months (OR 2.97; 95% CI, 1.01-8.71; .047) but not at 12 months (OR 1.12; 95% CI, 0.44-2.85).Incentive condition had no impact at any time point on the proportion of sent questionnaires that needed reminders. Odds of incomplete questionnaires were significantly greater at 3 months in the unconditional compared with the conditional incentive group (OR 2.45; 95% CI, 1.32-4.55; .004).Conclusions: Unconditional monetary incentives can produce a transitory greater likelihood of mailed questionnaire response in a clinical trial participant group, consistent with the direction of effect in other settings. However, this could have been a chance finding. The use of multiple strategies to promote response may have created a ceiling effect. This strategy has potential to reduce administrative and postage costs, weighed against the cost of incentives used, but could risk compromising the completeness of data.

Two-by-two factorial randomised study within a trial to evaluate strategies for follow-up in a randomised prevention trial

“…Hardy et al found no evidence that an unconditional incentive of a £10 gift voucher increased response to a postal questionnaire at one year in a trial of a maternal intervention at child birth (12). In contrast Young et al found that overall an unconditional incentive of a £5 gift voucher in a lung cancer screening trial in adults aged 50 to 75 did increase response although the questionnaire return was very high (> 90%) in both groups at all time points (one, 3, 6 and 12 months) (13). Since this SWAT started more SWATs of unconditional versus conditional trials of monetary incentives for retention have started (14), which are yet to report.…”

Two-by-two factorial randomised study within a trial (SWAT) to evaluate strategies for follow-up in a randomised prevention trial

“…Hardy et al found no evidence that an unconditional incentive of a £10 gift voucher increased response to a postal questionnaire at 1 year in a trial of a maternal intervention at child birth [12]. In contrast, Young et al found that overall an Data shown are n (%) using the number randomised to each group as the denominator unless otherwise specified SD standard deviation, SMS short message service a Host trial stratification variable unconditional incentive of a £5 gift voucher in a lung cancer screening trial in adults aged 50 to 75 years did increase response although the questionnaire return was very high (> 90%) in both groups at all time points (1, 3, 6 and 12 months) [13]. Since this SWAT started more SWATs of unconditional versus conditional trials of monetary incentives for retention have started [14], which are yet to report.…”

An Empirical Study of How Household Energy Consumption Is Affected by Co-Owning Different Technological Means to Produce Renewable Energy and the Production Purpose

“…To motivate the participants to complete the whole questionnaire, 5 Amazon vouchers were raffled. Doing so increases the response rate and statistical power in terms of representativity [43,44]. Ultimately 130,685 invitation e-mails were sent which resulted in 2074 completed questionnaires which entered the analysis.…”