Close this search box.

Addition of a diary (ID RET5)

Evidence Summary

What is it?

As opposed to the usual follow-up, participants receive a diary where they can record their experience.

Does it work?

Addition of a diary to usual follow-up probably reduces retention slightly.

How big is the effect?

An decrease of -3% (95% confidence interval = -4% to 2%).

How certain are we?

GRADE Moderate certainty.


We recommend that trialists add a diary to usual follow-up in the context of an intervention evaluation.

How can I use this straight away?

See Resource bundle below for details on how to add a diary to usual follow-up.

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 adding a diary to usual follow-up. The chart below shows the impact of an absolute decrease of -3% (95% CI = -2% to -4%). Retention is now 62%, which means our best estimate is that you would now be 18 responses short.

Cumulative Meta-Analysis*

*Random effects model done using Comprehensive Meta-Analysis v4 ( Differences >0% favour the intervention. The GRADE assessment is moderate because of imprecision.

Resource Bundle

How to Cite

Citation: Ostrovska B., Treweek S. Evidence pack– Retention: Addition of a diary to usual-follow up (RET5), 2023,

More Information

  1. This summary is from the Cochrane review of strategies to improve retention in randomised trials (
  2. The ‘Does it work?’ statement is structured according to effect size and GRADE certainty as per GRADE Guidelines 26 ( The statement is for small effect size and Moderate GRADE certainty.
  3. 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.
  4. If you have any questions contact
v1.0 - 05/07/2023
Scroll to Top