. 2021 Mar 6;2021(3):MR000032. doi: 10.1002/14651858.MR000032.pub3

Summary of findings 16. Impact of recruitment: optimised information vs standard information.

Addition of optimised information compared with standard information for trial retention
Patient or population: trial participants being followed up for data collection Settings: any setting Intervention: optimised patient information leaflet (PIL) Comparison: standard PIL
Outcomes	*Illustrative comparative risks (95% CI)**		Relative effect (95% CI)	No of Participants (studies)	Certainty of the evidence (GRADE)	Comments
	Assumed risk	Corresponding risk
	Optimised PIL	Standard PIL
Retention [follow‐up]	Low^a		RR 0.96 (0.85 to 1.09)	1285 (2)	⊕⊝⊝⊝ very low
	25 per 100	24 per 100 (21 to 27)
	Medium^a
	50 per 100	48 per 100 (43 to 55)
	High^a
	80 per 100	77 per 100 (68 to 87)
The basis for the assumed risk* (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; RR: risk ratio.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect.
^a We selected low, medium and high illustrative retention levels of 25%, 50% and 80% based on prior experience with trial retention and evidence from the literature. For example, it has been previously stated that it is common for up to 20% trial participants to drop out before the trial finishes (Walsh 2015), as such we set the upper limit of good retention as 80%. The other extreme of 25% was informed by evidence that some trials (largely internet based) can have retention as low as 10% to 25% (Murray 2009). The mid point of 50% was a judgement made by the review team and was deemed appropriate given the evidence for the other parameters.