Brueton, VC; (2015) Strategies to Improve Retention: Effectiveness and Use in Randomised Trials. Doctoral thesis , UCL (University College London).

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Abstract

Background Loss to follow-up from randomised trials (RCTs) can affect the reliability of results. Objectives To quantify the effect of strategies to improve retention in RCTs, explore their use, and develop best practice guidance. Methods Systematic review: including retention RCTs nested in RCTs. Qualitative study: in-depth interviews with RCT personnel. Consensus development: workshops with RCT personnel. Results Systematic review: 38 RCTs evaluated RCT retention strategies. Most aimed to improve questionnaire response. Questionnaire response was improved by: adding monetary incentives (RR 1.18;1.09-1.28), higher value monetary incentives (RR 1.12;1.04-1.22) and offering monetary incentives (RR 1.25;1.14-1.38). There is some evidence that recorded delivery (RR 2.08;1.11-3.87), a specialised postal strategy (RR 1.43;1.22-1.67) and an open RCT design (RR 1.37;1.16-1.63) also improve questionnaire response. There is no clear evidence that, when compared to usual follow-up procedures, questionnaire response / retention is improved by: sending questionnaires early, more disease-relevant questionnaires, shorter, or long and clear questionnaires, offering charity donations, giving or offering gifts, "enhanced" letters, priority post, additional reminders, questionnaire order, reminders to sites, behavioural or case management strategies. There was no clear effect for monetary incentives when compared to offering entry into a prize draw, or telephone surveys when compared to a monetary incentive with a questionnaire. Qualitative study: Communication and incentive strategies are routinely used to improve retention / response. There was uncertainty about their effectiveness. Non-monetary incentives, although used, were not thought to be effective. Efforts are made to improve questionnaire layout. Other strategies are seldom used. Factors thought to impact upon retention were identified. Consensus development: Best practice guidance was agreed for monetary incentives and postage. Conclusion Giving and offering small monetary incentives can be used to improve questionnaire response in RCTs. Second class postage can also be used. Application of the results would depend on RCT context and follow-up procedures.

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