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