Various return postage strategies (ID RET24)
Evidence Summary
What is it?
Various strategies compared to usual practice for return postage, such as free post versus second class stamp; high priority mail stamp versus usual postage; and personal form.
Does it work?
Various return postage strategies may increase retention slightly.
How big is the effect?
An increase of 4% (95% confidence interval = 0% to 9%).
How certain are we?
GRADE Low certainty.
Recommendation
We recommend that trialists consider using strategies such as free post, high priority mail among others for return postage.
How can I use this straight away?
See Resource bundle below for details on various return postage strategies.
Practical Impact
Imagine initial retention is 65% of those approached. 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 below).
Now imagine using different strategy for return postage. The chart below shows the impact of an absolute increase of 4% (95% CI = 0% to 9%). Retention is now 69%, which means our best estimate is that you would now be only 11 responses short.
Cumulative Meta-Analysis*
Resource Bundle
How to Cite
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 ‘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 small effect size and Low 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.
