The effectiveness of a contingent financial incentive to improve trial follow up; a randomised study within a trial (SWAT)

Research output: Contribution to journalArticlepeer-review


Objectives To evaluate the effectiveness of a contingent financial incentive (£10 note in addition to a routinely provided £10 voucher) versus no contingent financial incentive, on improving the retention rate in a randomised controlled trial (RCT). Methods A two arm 'Study within a Trial' (SWAT) embedded within a host RCT (SCIMITAR+). Participants were randomised to the SWAT using a 2:1 (intervention:control) allocation ratio. The primary outcome measure was the proportion of participants completing a CO breath measurement at the first SCIMITAR+ follow up time point (6 months). Secondary outcomes were withdrawing from follow-up after contact and time from assessment due date to completion. Analyses were conducted using logistic or Cox Proportional Hazards regression as appropriate. Results A total of 434 participants were randomised into this SWAT. Completion of the CO breath measurement at 6 months was 88.5% (n=247) in the intervention arm of the SWAT and 85.4% (n=123) in the control arm (Difference 3.1%, OR 1.29, 95% CI 0.71-2.33, p=0.41). There was also no evidence of a difference in the proportion of participants withdrawing from follow-up after contact (intervention n=7 (2.5%), control n=5 (3.5%); OR 0.76, 95% CI 0.23-2.44, p=0.64), nor in terms of proximity of 6-month visit completion to due date (HR 1.07, 95% CI 0.86-1.33, p=0.55). Conclusion It is unclear if contingent financial incentives increased rates of face-to-face follow-up completion within the SCIMITAR+ trial population. However, the sample size of this SWAT was constrained by the size of the host trial and power was limited. This SWAT adds to the body of evidence for initiatives to increase response rates in trials.

Original languageEnglish
Article number1937
Number of pages14
Publication statusPublished - 17 Jul 2020

Bibliographical note

Funding Information:
Grant information: This work was conducted as part of the SCIMITAR ਀ Trial which was funded by the NIHR Health Technology Assessment Programme (11/136/52). The views expressed are those of the author(s) and not necessarily those of the NIHR of the Department of Health and Social Care.

Publisher Copyright:
© 2020 Arundel C et al.


  • Randomized controlled trial
  • Retention
  • SWAT

Cite this