Increasing response rates to postal questionnaires: systematic review

<h3>Abstract</h3> <b>Objective:</b> To identify methods to increase response to postal questionnaires. <b>Design:</b> Systematic review of randomised controlled trials of any method to influence response to postal questionnaires. <b>Studies reviewed:</b> 292 randomised controlled trials including 258 315 participants <b>Intervention reviewed:</b> 75 strategies for influencing response to postal questionnaires. <b>Main outcome measure:</b> The proportion of completed or partially completed questionnaires returned. <b>Results:</b> 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). <b>Conclusions:</b> Health researchers using postal questionnaires can improve the quality of their research by using the strategies shown to be effective in this systematic review. <h3>What is already known on this topic</h3> 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 <h3>What this study adds</h3> 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 <i>Cochrane Library</i>