Evidence Summary

What is it?

A pen sent with trial questionnaire and/or study materials, which serves as a reminder to return study items. The pen can contain the research institution details and/or the trial name and logo

Does it work?

Sending a trial pen probably increases retention and response rate.

How big is the effect?

An increase of 2% (95% confidence interval = 0% to 4%).

How certain are we?

GRADE Moderate certainty.

GRADE High certainty for an older population.


We recommend that trialists send pens to participants to increase retention in trials that use questionnaires.

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 including a pen with the questionnaires. The chart below shows the impact of an absolute increase of 2% (95% CI = 0% to 4%). Retention is now 66%, which means our best estimate is that you would now only be 13 responses short.

Cumulative Meta-Analysis*

*Random effects model done using Comprehensive Meta-Analysis v3 (www.meta-analysis.com).
Differences >0% favour the intervention. The GRADE assessment is moderate.

Resource Bundle


How to Cite

Citation: Clark L, Coleman E, Arundel C, Doherty L, Torgerson D. Evidence pack– Retention: Including a pen with study materials (Ret3), 2020, https://www.trialforge.org/retention-sector/including-a-pen-with-study-materials/

More Information

  1. The majority of the data in this summary is from the PROMETHEUS project (https://www.york.ac.uk/healthsciences/research/trials/research/swats/prometheus/).
  2. 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
  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 info@trialforge.org.
Version: v1.0 - 7/5/2020

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