An approach to developing successful trial follow-up procedures
Randomised controlled trials are considered the gold standard for evaluation but can be subject to bias caused by losses to follow up. Almost half of trials fail to achieve their follow up target. Systematic reviews of trials have identified effective interventions to increase follow-up, but guidance for developing follow up procedures has not been generated. This paper reports on an approach to developing trial follow-up procedures used in a pilot randomised controlled trial of our sexual health intervention delivered by text message.
In the trial, two hundred people aged 16-24 were randomised to receive the safer sex intervention or control, both delivered by text message. We collected questionnaire outcome data at one month and 12 months and chlamydia test samples at three and 12 months. We developed follow up procedures based on evidence, testing and user views. We identified evidence-based methods to increase follow-up reported in systematic reviews. We tested prototype follow-up procedures to identify barriers to follow-up completion and to generate procedures that were as easy as possible to complete. We sought potential participant views regarding follow-up procedures. We tested all the new procedures.
Strategies that we developed to overcome barriers to completion included using packaging that fits through letterboxes, sending materials in coloured envelopes so that participants could recognised them and using simplified test sample instructions and materials. Overall, out of 200 participants, 92% (n= 183) provided questionnaire outcome data at one month; 86% (n=171) returned a chlamydia test sample at three months; 81% (n= 162) provided questionnaire outcome data and 80% (n= 159) returned a chlamydia test sample at 12 months.
Our approach provides a simple stepwise guide to developing trial follow up procedures that could be adopted by other researchers. Using this approach we achieved high follow-up for postal chlamydia tests, while response rates for postal chlamydia samples in previous trials have been 50% or less. Follow-up in other trials may benefit from adopting this approach.
- Ona McCarthy
- Rebecca French
- Caroline Free