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Timing of Short Messaging Service (SMS) Reminders did not Improve Trial Participant Questionnaire Return: An Embedded Randomized Trial and Meta-Analysis

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Publication details

JournalJournal of Clinical Epidemiology
DateAccepted/In press - 16 Oct 2019
Original languageEnglish


To assess whether timing of SMS reminders improved postal questionnaire return rates from participants in a randomized controlled trial (RCT). Study Design and Setting: A Study Within A Trial (SWAT) embedded in a multicentre
RCT evaluating three treatments for frozen shoulder. Participants who provided a mobile telephone number were randomized to either pre-notification SMS on the day of the questionnaire mail-out or post-notification SMS four days following questionnaire mail out for the three-month follow-up. The primary outcome was the proportion of participants who returned a valid questionnaire. A systematic review was undertaken to identify other embedded trials to perform a meta-analysis.

Results: Of the 269 participants, 122/135 (90.4%) returned a valid questionnaire in the pre-notification arm and 119/134 (88.8%) in the post-notification arm (difference of -1.6%; 95% CI of difference: -8.9%, 5.7%). There was no difference in time to response (HR=1.04; 95% CI: 0.80 to 1.34) or need for additional reminders (OR=0.71; 95% CI: 0.43 to 1.17). Meta-analysis of two RCTs showed no difference in response rates between pre and post-notification reminders (OR=0.78 95% CI: 0.42 to 1.45). Conclusion: Timing of SMS reminders did not improve response rates, time to response or affect the need for additional reminders.

Randomized controlled trial; SMS; text message; retention; study within a trial;

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