Substantial amounts of public funds are invested in health research worldwide. Publicly funded randomised controlled trials (RCTs) often recruit participants at a slower than anticipated rate. Many trials fail to reach their planned sample size within the envisaged trial timescale and trial funding envelope. A team of DTS staff and students led, by Stephen Walters, reviewed 787 reports published in the National Institute for Health Research (NIHR) Health Technology Assessment (HTA) Journal between 2004 and 2016.

The review identified 151 individually randomised controlled trials from 787 NIHR HTA reports and found that the final recruitment target sample size was achieved in 56% (85/151) of the RCTs and more than 80% of the final target sample size was achieved for 79% of the RCTs (119/151).

The median recruitment rate (participants per centre per month) was found to be 0.92 (Interquartile range (IQR) 0.43 to 2.79) and the median retention rate (proportion of participants with valid primary outcome data at follow-up) was estimated at 89% (IQR 79% to 97%).

The review has been published in the BMJ Open in March 2017 and presented as poster at the 4th International Clinical Trials Methodology Conference, held jointly with the Society for Clinical Trials Annual Meeting, in Liverpool, in May 2017; where the work was citied in a plenary session of the conference by the Director of the HTA Programme, Professor Hywel Williams. This work, which was only published in March 2017 has an Altmetric score of 28 (which would place it the top 5% of all research outputs scored by Altmetric); and has been widely disseminated on social media.

There is considerable variation in the consent, recruitment and retention rates in publicly funded RCTs. Investigators should bear this in mind at the planning stage of their study and not be overly optimistic about their recruitment projections.