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Introduction: Poor retention in clinical trials can impact on statistical power, reliability, validity and generalisability of findings and is a particular challenge in smoking cessation studies. In online trials with automated follow up mechanisms, poor response also increases resource-need for manual follow up. This study compared two financial incentives on response rates at 6 months follow up, in an online, automated smoking cessation feasibility trial of a cessation smartphone app (Quit Sense).

Methods: A study within a trial (SWAT), embedded within a host randomised controlled trial. Host trial participants were randomised 1:1 to receive either a £10 or £20 voucher incentive, for completing the 6-month questionnaire. Stratification for randomisation to the SWAT was by minimisation to ensure an even split of host trial arm participants, and by 6-week response rate. Outcome measures were: questionnaire completion rate, time to completion, number of completers requiring manual follow up and completeness of responses.

Results: 204 participants were randomised to the SWAT. The £20 and £10 incentives did not differ in completion rate at 6 months (79% versus 74%; p=0.362) but did reduce the proportion of participants requiring manual follow up (46% versus 62%; p=0.018) and the median completion time (7 days versus 15 days; p=0.008). Measure response completeness rates were higher among £20 incentive participants, though differences were small for the host trial's primary smoking outcome.

Conclusions: Benefits to using relatively modest increases in incentive for online smoking cessation trials include more rapid completion of follow up questionnaires and reduced manual follow up.

Implications: A modest increase in incentive (from £10 to £20) to promote the completion of follow up questionnaires in online smoking cessation trials may not increase overall response rates but could lead to more rapid data collection, a reduced need for manual follow-up and reduced missing data among those who initiate completing a questionnaire. Such an improvement may help to reduce bias, increase validity and generalisability, and improve statistical power in smoking cessation trials.
Original languageEnglish
JournalNicotine and Tobacco Research
Publication statusE-pub ahead of print - 21 Mar 2024

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