"Bird in the hand" cash was more effective than prize draws in increasing physician questionnaire response

To investigate the effects of two monetary incentives on response rates to postal questionnaires from primary care physicians (PCPs).

The PCPs were randomized into three arms (n=550 per arm), namely (1) €5 sent with the questionnaire (cash); (2) entry into a draw on return of completed questionnaire (prize); or (3) no incentive. Effects of incentives on response rates and item nonresponse were examined, as was cost-effectiveness.

Response rates were significantly higher in the cash (66.1%; 95% confidence interval [CI]: 61.9, 70.4%) and prize arms (44.8%; 95% CI: 40.1, 49.3%) compared with the no-incentive arm (39.9%; 95% CI: 35.4, 44.3%). Adjusted relative risk of response was 1.17 (95% CI: 1.02, 1.35) and 1.68 (95% CI: 1.48, 1.91) in the prize and cash arms, respectively, compared with the no-incentive group. Costs per completed questionnaire were €9.85, €11.15, and €6.31 for the cash, prize, and no-incentive arms, respectively. Compared with the no-incentive arm, costs per additional questionnaire returned in the cash and prize arms were €14.72 and €37.20, respectively.

Both a modest cash incentive and entry into a prize draw were effective in increasing response rates. The cash incentive was most effective and the most cost-effective. Where it is important to maximize response, a modest cash incentive may be cost-effective.