Pick your certainty level
Using opt-out consent rather than opt-in consent may improve recruitment
Having an open rather than a blinded placebo trial increases recruitment.
Telephone reminders probably increase recruitment.
Enclosing a questionnaire covering issues relevant to trial with the invitation probably increases recruitment.
Financial incentives probably increase recruitment slightly.
Giving quotes from existing participants in text messages probably increases recruitment slightly.
Mentioning scarcity of trial places in text messages probably increases recruitment slightly.
Optimising the participant information leaflet (PIL) through a particular, bespoke process involving formal user testing makes little or no difference to recruitment.
Email invitations probably result in little to no difference in recruitment compared to postal invitations but is cheaper to use.
Recruitment at a church and other enhancements may increase recruitment.
Brief PILs make little or no difference to recruitment.
Enhanced recruitment including more contact by African Americans may have little or no effect on recruitment to a trial involving African Americans.
Enhanced recruitment including more telephone contact by African Americans may have little or no effect on recruitment to a trial involving African Americans.
Emphasising risk in participant information may have little or no effect on recruitment to a trial.
Optimising the PIL through using user feedback probably makes little or no difference in recruitment.
Using a postcard teaser campaign made little or no difference to recruitment.
Sending a recruitment primer letter may have little or no effect on recruitment.
Providing participant information over the telephone rather than face-to-face may have little or no effect on recruitment.
Top 5 Recruitment Tips
Opt-out, rather than opt-in, procedures may improve recruitment where it can be done. There’s only one evaluation so replication studies would be useful.
Having an open, rather than a blinded trial improves recruitment. The downside is that lack of blinding brings its own problems with outcome assessment.
Telephone reminders to non-responders. Decent evidence but in trials with very low initial recruitment. Replication studies would help.
Enclosing a questionnaire covering issues relevant to the trial together with the invitation. Only one evaluation so replication would be useful.
Financial incentives. Odds-on that this is effective but some inconsistency in effect. Replication needed.
More About Recruitment
Trials across the world struggle to recruit sufficient participants in the timescale originally defined for recruitment activity. This can result in recruitment time extensions and/or extensions to the trial budget; it is important to note that an extension denoted strictly to time is not necessarily a ‘free’ extension and may result in opportunity lost costs for the trial team and units involved. Trial extensions may delay the availability of beneficial interventions to the public, or could result in harmful or useless interventions being used for longer time periods than is ethically necessary.
If recruitment fails to successfully reach the target sample size, the likelihood of finding no statistically significant difference between outcomes where one does in fact exist, is heightened; this is referred to as a type II error.
In the worst cases trials can be abandoned as a result of poor recruitment, costing large amounts of money and leaving the research question unanswered.
Trial Forge is actively working on improving the evidence base around recruitment of trial participants; if you would like to collaborate on an embedded study focussed on recruitment strategies please get in touch.
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