Evidence Summary

What is it?

The patient consent form describes a randomised trial of usual treatment vs new medication as “may work twice as fast as the usual treatment” instead of “may work half as fast as the usual treatment).

Does it work?

Writing treatment effect as 'twice as fast' rather than 'half as fast' may improve recruitment.

How big is the effect?

An increase of 26% (95% confidence interval = 7% to 45%).

How certain are we?

GRADE Low certainty.


We recommend that trialists consider using different wording for new treatment options where appropriate.

How can I use this straight away?

See Resource bundle below for details on how to use different wording for treatment effects.

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 describing a treatment effect as “twice as fast”. The chart below shows the impact of an absolute increase of 26% (95% CI = 7% to 45%). Recruitment is now 56%, which means our best estimate is that 54 people would now need to be approached to recruit 30 of them.

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 low because of the imprecision of a single study.

Resource Bundle


How to Cite

Citation: Ostrovska B., Evidence pack­– Recruitment: Describing a treatment effect as ‘twice as fast’ (REC20), 2023, https://www.trialforge.org/recruitment-sector/describing-a-treatment-effect-as-twice-as-fast-id-rec20

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 a large effect size and GRADE Low 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

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