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Table 2 Effect of strategies that involved a change in mode of data collection

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)
Johnson 2015 [28] Before and after study Unique hyperlink to the follow-up questionnaire plus reminders sent at 2-week intervals (6 months after randomisation) Telephone follow-up to non-resonders (4 weeks later) Retention before telephone follow-up was 62.1% (520/837) and 82.8% (693/837) afterward: an increase of 20.7% (173/837) No secondary end point reported
Childs 2015 [26] Before and after study 3-monthly web-based surveys sent 2 years following completion of the assigned intervention A telephone follow-up to non-responders at the end of the first year Adding the telephone call center resulted in an 18.6% increase in follow-up rate No secondary end point reported
Dormandy 2008 [27] Before and after study Postal questionnaire completion only A choice of telephone or postal questionnaire completion The response rate (11 months after randomisation) from women offered postal completion was 26% compared with 67% for women offered a choice of telephone or postal completion (41% difference). Response rate for women choosing telephone completion was 98% compared with 23% for women choosing postal completion (75% difference, 95% CI diff 70 to 80) No secondary end point reported
Lall 2012 [29] Prospective cohort study Postal questionnaire completion 12 months after randomisation. Telephone follow-up to nonrespondents (6 weeks later) The overall response rate increased by 14% (from 71 to 85%) after telephone follow-up No secondary end point reported
Atherton 2010 [25] Prospective cohort study Postal questionnaire completion after 12 months Online questionnaire The response rates to the 12-month questionnaire in the online and postal groups were 51% and 29%, respectively, 4 weeks after follow-up commenced (RR 1.78 (1.47 to 2.14)) The response rates to the 12-month questionnaire in the online and postal groups were 72% and 59%, respectively, after 3 months
Peterson 2012 [30] Post hoc analysis method Routine follow-up Home follow-up Home follow-up (6 months after randomisation) was effective in achieving follow-up on an additional 61 participants (25%), decreasing attrition rate to only 4% No secondary end point reported