What impact do monetary incentives and questionnaire length have on mailed health psychology survey response?

Abstract

Background: Response rates to health-related surveys are declining. This study tested two strategies to improve the response rate to a health psychology survey mailed through general practices: 1) sending a shortened questionnaire; and 2) offering a monetary incentive to return a completed questionnaire. Methods: Adults (n=4,241) aged 45-59 years, from four general practices in south-east England were mailed a survey on attitudes towards bowel cancer screening. Using a 2x4 factorial design, participants were randomised to receive: (1) a ‘short’ (4 A4 pages) or ‘long’ (7 A4 pages) questionnaire; and (2) one of four monetary incentives to return a completed questionnaire - i) no monetary incentive, ii) £2.50 shop voucher, iii) £5.00 shop voucher, iv) inclusion in a £250 shop voucher prize draw. Age, gender and area-level deprivation were obtained from the general practices. Findings: The overall response rate was 44.0%. The ‘long’ questionnaire (43.5%) had no effect on response rate when compared to the ‘short’ questionnaire (44.4%; OR= 0.97 [0.85, 1.09]). The £5.00 (45.2%) and £250 prize draw (43.2%) incentives had no significant impact on response rates compared to no incentive (41.5%). The £2.50 incentive (45.9%) significantly improved response rates in univariate analyses (OR= 1.20 [1.01, 1.42]), however this did not remain significant after controlling for age, gender, area-level deprivation and questionnaire length. Discussion: Prize draws are frequently used to incentivise participation in surveys but in this study they had no impact on response rate. Interestingly, a ‘long’ questionnaire did not decrease response relative to a ‘short’ questionnaire.