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Table 3 Effect of strategies that used a change in mode of reminders delivery

From: Non-randomised evaluations of strategies to increase participant retention in randomised controlled trials: a systematic review

Study ID Study design Comparator Intervention Difference in response rate (primary end point) Difference in response rate (secondary end point)
Hansen 2014 [33] Prospective cohort study A follow-up questionnaire and up to two reminders by mail Non-responders were contacted by telephone to return postal questionnaires Telephone contact (1 year follow-up after randomisation) raised the response by 10% from 316 (64%) to 364 (74%) No secondary end point reported
Varner 2017 [39] Prospective cohort study Participants were contacted by a conventional telephone call during the 4 months of study follow-up Non-responders (final 3 months) were sent text message reminders of upcoming telephone follow-up for the return of postal questionnaires. Sending text messages increased response by 22% (95% CI 5.9 to 34.7%) at 2-week follow-up Sending text messages increased response by 17.7% (95% CI − 0.8 to 33.3%) at 4-week follow-up