Mentioning scarcity of trial places in text messages.
Mentioning scarcity of trial places in text messages probably increases recruitment slightly.
An increase of 3% (95% confidence interval = 1% to 6%).
GRADE Moderate certainty.
We suggest that trialists consider using text messaging #1: mentioning scarcity, ideally as part of a SWAT evaluation
See Resource bundle below for details of how to use text messaging #1: mentioning scarcity or build a SWAT evaluation of them into your trial.
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 mentioning scarcity in a text message. The chart below shows the impact of an absolute increase of 3% (95% CI = 1% to 6%). Recruitment is now 3%, which means our best estimate is that 91 people would now need to be approached to recruit 30 of them.