Evidence Summary
What is it?
Tell participants in the first mailing of the questionnaire that they will receive a £10 voucher if they return their questionnaire.
Does it work?
Telling participants they will receive a financial incentive if they return a questionnaire probably increases retention.
How big is the effect?
An increase of 9% (95% confidence interval = 3% to 15%).
How certain are we?
GRADE Moderate certainty.
Recommendation
We suggest that trialists consider using financial incentives, ideally as part of a SWAT evaluation.
How can I use this straight away?
See Resource bundle below for details of how to use financial incentives or build a SWAT evaluation of them into your trial.
Practical Impact
Imagine initial retention is 65%. You have a trial with 100 participants that needs responses from 80 to meet its statistical power calculations. Retention of 65% means that you will be 15 responses short (see chart).
Now imagine using financial incentives. The chart below shows the impact of an absolute increase of 9% (95% CI = 3% to 15%). Retention is now 74%, which means our best estimate is that you would now only be 6 responses short.
Cumulative Meta-Analysis*
*Fixed effects model done using Comprehensive Meta-Analysis v3 (www.meta-analysis.com).
Differences >0% favour the intervention. The GRADE assessment is moderate because of imprecision due to being a single study.
Resource Bundle
How to Cite
Citation: Treweek S, Bruhn H. Evidence pack– Retention: Financial incentives as a way to avoid reminders for questionnaire return (Ret4), 2021, https://www.trialforge.org/recruitment-sector/having-an-open-rather-than-blinded-trial/.
More Information
- This summary is from the Cochrane review of strategies to improve retention in randomised trials (https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.MR000032.pub3/full).
- The summary was prepared with financial support from Evidence Synthesis Ireland.
- The ‘Does it work?’ statement is structured according to effect size and GRADE certainty as per GRADE Guidelines 26 (https://doi.org/10.1016/j.jclinepi.2019.10.014). The statement is for moderate effect size and High GRADE certainty.
- The recommendation statement is the consensus view of the authors of this summary based on the GRADE certainty and features of the trials contributing to the evidence.
- If you have any questions contact info@trialforge.org.
