Recruitment, consent and retention of participants in randomised controlled trials: a review of trials published in the National Institute for Health Research (NIHR) Journals Library (1997–2020)

Abstract

ObjectivesTo review the consent, recruitment and retention rates for randomised controlled trials (RCTs) funded by the UK’s National Institute for Health Research (NIHR) and published in the online NIHR Journals Library between January 1997 and December 2020.DesignComprehensive review.SettingRCTs funded by the NIHR and published in the NIHR Journals Library.Data extractionInformation relating to the trial characteristics, sample size, recruitment and retention.Primary and secondary outcome measuresThe primary outcome was the recruitment rate (number of participants recruited per centre per month). Secondary outcomes were the target sample size and whether it was achieved; consent rates (percentage of eligible participants who consented and were randomised) and retention rates (percentage of randomised participants retained and assessed with valid primary outcome data).ResultsThis review identified 388 individual RCTs from 379 reports in the NIHR Journals Library. The final recruitment target sample size was achieved in 63% (245/388) of the RCTs. The original recruitment target was revised in 30% (118/388) of trials (downwards in 67% (79/118)). The median recruitment rate (participants per centre per month) was found to be 0.95 (IQR: 0.42–2.60); the median consent rate was 72% (IQR: 50%–88%) and the median retention rate was estimated at 88% (IQR: 80%–97%).ConclusionsThere is considerable variation in the consent, recruitment and retention rates in publicly funded RCTs. Although the majority of (6 out of 10) trials in this review achieved their final target sample; 3 out of 10 trials revised their original target sample size (downwards in 7 out of 10 trials). Investigators should bear this in mind at the planning stage of their study and not be overly optimistic about their recruitment projections.

Improving sleep apnea treatment adherence after traumatic brain injury: A nonrandomized feasibility study.

“…The retention rate in this study (76.5%) was near retention rates reported in a review of published randomized controlled trials from 1997–2020 (median = 88%, range = 0–100%; Jacques et al, 2022). It appeared that those who withdrew had less severe OSA based on visual data inspection (fewer reported average baseline symptoms) and were more likely to be classified as having severe disability.…”

“…Of persons who met all inclusion criteria, the consent rate was 51.5% that was lower than rates reported in a review of published randomized controlled trials from 1997–2020 (median = 72%, range = 4–100%) although these included medication-based trials (Jacques et al, 2022) and were not OSA-specific treatment studies. In this study, the predominant reason for nonenrollment among those eligible was lack of concern about their OSA (43.8%) followed by the time commitment (31.3%).…”

A good use of time? Providing evidence for how effort is invested in primary and secondary outcome data collection in trials

“…We might accept some of this if all trials nished on time, to budget and published all their data but we know this is not true. Recruitment and retention problems are widespread 17,18 , the cost of trials is escalating 1 and substantial amounts of data never make it into the public domain 6 . A study evaluating trials funded by the UK's National Institute for Health Research Health Technology Assessment Programme, a highly competitive funding stream, found that between 1997 and 2020, 128/388 (33%) of trial teams needed to extend their recruitment period 17 .…”

“…Recruitment and retention problems are widespread 17,18 , the cost of trials is escalating 1 and substantial amounts of data never make it into the public domain 6 . A study evaluating trials funded by the UK's National Institute for Health Research Health Technology Assessment Programme, a highly competitive funding stream, found that between 1997 and 2020, 128/388 (33%) of trial teams needed to extend their recruitment period 17 . Only 207/388 (53%) reached 100% of the original recruitment target and median retention for the primary outcome was 88%.…”

A good use of time? Providing evidence for how effort is invested in primary and secondary outcome data collection in trials

“…We might accept some of this if all trials finished on time, to budget and published all their data but we know this is not true. Recruitment and retention problems are widespread [ 17 , 18 ], the cost of trials is escalating [ 1 ] and substantial amounts of data never make it into the public domain [ 6 ]. A study evaluating trials funded by the UK’s National Institute for Health Research Health Technology Assessment Programme, a highly competitive funding stream, found that between 1997 and 2020, 128/388 (33%) of trial teams needed to extend their recruitment period [ 17 ].…”