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Pen at recruitment (ID RET6)

Evidence Summary

What is it?

Including a pen with the trial invitation pack. The pen can contain the research institution details and/or the trial name and logo.

Does it work?

Giving a pen at recruitment probably increases retention.

How big is the effect?

An increase of 20% (95% confidence interval = 7% to 32%).

How certain are we?

GRADE Moderate certainty.


We recommend that trialists include a pen with the trial invitation pack sent to participants.

How can I use this straight away?

See Resource bundle below for support materials.

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 giving a pen at recruitment. The chart below shows the impact of an absolute increase of 20% (95% CI = 7% to 32%). Retention is now 85%, which means our best estimate is that you would now have enough participants to meet the statistical power calculations.

Cumulative Meta-Analysis*

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

Resource Bundle

How to Cite

Citation: Ostrovska B. Evidence pack– Retention: Pen at recruitment (RET6), 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 moderate 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 - 06/07/2023
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