Emphasising risk in participant information

Emphasising risk in participant information may make little or no difference in recruitment.


The absolute increase is 0% (95% CI = -1% to 0%)1

How confident are we in the evidence?  
What is GRADE?

LOW CERTAINTY in the evidence (but see 'What we don't know' below)

1 Treweek S, Pitkethly M, Cook J, Fraser C, Mitchell E, Sullivan F, Jackson C, Taskila TK, Gardner H. Strategies to improve recruitment to randomised trials. Cochrane Database of Systematic Reviews 2018, Issue 2.

The practical impact of emphasising risk in participant information

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 (see chart below).

No risk emphasis
No risk emphasis

Now imagine recruiting using information that emphasises risk in the trial. The chart below shows the impact of an absolute increase of 0% (95% CI =-1% to 0%)1. Recruitment is still 30%, which means our best estimate is still that 100 people would need to be approached to recruit 30 of them.

With risk emphasis
With risk emphasis
By using enhanced recruitment including more contact, our best estimate is that you will need to approach the same number of people as without the enhancement.

Where has emphasising risk in participant informations been tested?


Mentioning that procedure had some risk (note that the trial was hypothetical, although participants were not told this until after their decision)


Told procedure was harmless


1 study including a total of 97 participants

Study 1: Treschan 2003

Patients were undergoing minor surgery with general anaesthetic, 19 to 80 years old. They were asked to take part in a trial, which turned out to be hypothetical but they were not told this until they had made a decision about they willingness total part

Trial intervention?
Extra oxygen during and immediately after surgery (but hypothetical as it turned out).

Study location?
Secondary care, Austria.

What difference?
26% of participants randomised to hearing more about risk would be willing to participate; 64% of participants told the procedure was harmless would be willing to participate

Read more about this study here.

What we still don’t know about emphasising risk in participant informationt

  • The GRADE assessment is low for this intervention because the risk of bias was unclear and there is only a single evaluation. More evaluations in any type of trial are needed.
  • Please get in touch (email info@trialforge.org) if you would like to do an evaluation because we can help with text for ethics etc.

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