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

OBJECTIVES: 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 English general practices: (1) sending a shortened questionnaire and (2) offering a monetary incentive to return a completed questionnaire. DESIGN: Randomized controlled trial. 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 2 × 4 factorial design, participants were randomized to receive a ‘short’ (four A4 pages) or a ‘long’ (seven A4 pages) questionnaire, and one of four monetary incentives to return a completed questionnaire – (1) no monetary incentive, (2) £2.50 shop voucher, (3) £5.00 shop voucher, and (4) inclusion in a £250 shop voucher prize draw. Age, gender, and area‐level deprivation were obtained from the General Practices. RESULTS: The overall response rate was 41% (n = 1,589). Response to the ‘short’ questionnaire (42%) was not significantly different from the ‘long’ questionnaire (40%). The £2.50 incentive (43%) significantly improved response rates in univariate analyses, and remained significant after controlling for age, gender, area‐level deprivation, and questionnaire length. The £5.00 (42%) and £250 prize draw (41%) incentives had no significant impact on response rates compared to no incentive (38%). CONCLUSIONS: A small monetary incentive (£2.50) may slightly increase response to a mailed health psychology survey. The length of the questionnaire (four pages vs. seven pages) did not influence response. Although frequently used, entry into a prize draw did not increase response. Achieving representative samples remains a challenge for health psychology. STATEMENT OF CONTRIBUTION: What is already known on this subject Response rates to mailed questionnaires continue to decline, threatening the representativeness of data. Prize draw incentives are frequently used but there is little evidence to support their efficacy. Research on interactions between incentives, questionnaire length, and demographics is lacking. What does this study add Contrary to previous findings, questionnaire length did not influence response rate. A £2.50 incentive increased response, while incentives of £5.00 and a £250 prize draw did not. Achieving representative samples to questionnaires remains a challenge for health psychology.