PROMoting the use of studies within a trial (PROMETHEUS): Results and experiences from a large programme to evaluate the routine embedding of recruitment and retention strategies within randomised controlled trials routinely.

Aim: PROMoting THE USE of Studies Within A Trial (PROMETHEUS) aimed to improve the evidence base for recruiting and retaining participants in Randomised Controlled Trials (RCTs) by pump-priming and facilitating the start of at least 25 Studies Within A Trial (SWATs) testing recruitment or retention interventions. Methods: Ten Clinical Trials Units (CTUs) and one Primary Care Research Centre formed a network to conduct randomised SWATs of recruitment and/or retention strategies. We identified promising recruitment and retention interventions from various sources, which were reviewed by patient and public (PPI) partners to generate an initial priority list of seven recruitment and eight retention interventions.Host trial teams could apply for funding of up to £5000 and receive support from the PROMETHEUS team to design, implement, and report SWATs. We additionally tested the feasibility of undertaking coordinated SWATs across multiple host trials simultaneously. Results: PROMETHEUS funded 42 SWATs, embedded within 31 host trials, across 12 CTUs. The SWAT cost per SWAT was £3535. Of the 42 SWATs, 12 tested the same SWAT in multiple trials ( Conclusion: The PROMETHEUS programme substantially increased the evidence base for both recruitment and retention strategies within RCTs. Future research should adopt a systematic approach to identifying and targeting gaps in the evidence base and focus on translating SWAT evidence into recruitment and retention practice.