Increasing response rates to postal questionnaires: systematic review

Abstract Objective: To identify methods to increase response to postal questionnaires. Design: Systematic review of randomised controlled trials of any method to influence response to postal questionnaires. Studies reviewed: 292 randomised controlled trials including 258 315 participants Intervention reviewed: 75 strategies for influencing response to postal questionnaires. Main outcome measure: The proportion of completed or partially completed questionnaires returned. Results: The odds of response were more than doubled when a monetary incentive was used (odds ratio 2.02; 95% confidence interval 1.79 to 2.27) and almost doubled when incentives were not conditional on response (1.71; 1.29 to 2.26). Response was more likely when short questionnaires were used (1.86; 1.55 to 2.24). Personalised questionnaires and letters increased response (1.16; 1.06 to 1.28), as did the use of coloured ink (1.39; 1.16 to 1.67). The odds of response were more than doubled when the questionnaires were sent by recorded delivery (2.21; 1.51 to 3.25) and increased when stamped return envelopes were used (1.26; 1.13 to 1.41) and questionnaires were sent by first class post (1.12; 1.02 to 1.23). Contacting participants before sending questionnaires increased response (1.54; 1.24 to 1.92), as did follow up contact (1.44; 1.22 to 1.70) and providing non-respondents with a second copy of the questionnaire (1.41; 1.02 to 1.94). Questionnaires designed to be of more interest to participants were more likely to be returned (2.44; 1.99 to 3.01), but questionnaires containing questions of a sensitive nature were less likely to be returned (0.92; 0.87 to 0.98). Questionnaires originating from universities were more likely to be returned than were questionnaires from other sources, such as commercial organisations (1.31; 1.11 to 1.54). Conclusions: Health researchers using postal questionnaires can improve the quality of their research by using the strategies shown to be effective in this systematic review. What is already known on this topic Postal questionnaires are widely used in the collection of data in epidemiological studies and health research Non-response to postal questionnaires reduces the effective sample size and can introduce bias What this study adds This systematic review includes more randomised controlled trials than any previously published review or meta-analysis no questionnaire response The review has identified effective ways to increase response to postal questionnaires The review will be updated regularly in the Cochrane Library