Evidence Summary

What is it?

A series of postcards that depict the trial logo and research institute logos are mailed out. One of the postcards has a statement similar to “look out for your invitation letter in the coming weeks…” with contact details. A week later, the standard approach to recruitment with formal invitation letters is commenced.

Does it work?

Using a postcard teaser campaign made little or no difference to recruitment.

How big is the effect?

An increase of 0% (95% confidence interval = -4% to 5%).

How certain are we?

GRADE Moderate certainty.


We recommend that trialists use postcard teaser campaigns in the context of an intervention evaluation.

How can I use this straight away?

See Resource bundle below for details on how to implement a postcard teaser campaign.

Practical Impact

Imagine a trial that needs to recruit 30 participants and initial recruitment is 30% of those approached. This means you’d need to approach 100 people to recruit 30 of them (see chart).


Now imagine using a postcard teaser campaign. The chart below shows the impact of an absolute increase of 0% (95% CI = -4% to 5%). Recruitment is still 30%, which means our best estimate is that 100 people would still need to be approached to recruit 30.

Cumulative Meta-Analysis*

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

Resource Bundle


How to Cite

Citation: Treweek S, Bruhn H, Gardner H. Evidence pack­– Recruitment: Postcard teaser campaign (REC23), 2023, https://www.trialforge.org/recruitment-sector/postcard-teaser-campaign-id-rec23/

More Information

  1. This summary is from the Cochrane review of strategies to improve recruitment in randomised trials (https://doi.org/10.1002/14651858.MR000013.pub6).
  2. It was prepared with financial support from Evidence Synthesis Ireland.
  3. 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 trivial, small unimportant effect or no effect and GRADE Moderate certainty.
  4. 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.
  5. If you have any questions contact info@trialforge.org.
Version: v2.0 - 10/07/2023

Start typing and press Enter to search