Follow-up by mail in clinical trials: does questionnaire length matter?

In large clinical trials where outcome assessment is possible using questionnaires, it may be more cost-effective to mail them to patients than to conduct interviews in-person. However, nonresponse to mailed questionnaires reduces the effective sample size and can introduce bias. We conducted a systematic review and meta-analysis of randomized controlled trials evaluating the effect of questionnaire length on response rates. We searched 14...