Text message reminders to improve questionnaire response rates in RCTs: findings from three randomised sub-studies

Methods Three randomised sub-studies were embedded in the UK ACUDep trial at three follow-up points. 523 patients of 755 in the main trial consented to being contacted by text message and were randomised to a pre-questionnaire reminder or no reminder at 3 months, a pre-reminder or post-reminder at 6 months and a post-reminder or no reminder at 9 months. Chi square tests and time-to event analyses were used to assess attrition between groups.