Factors distinguishing general practitioners who more readily participated in a large randomized trial were identified.

OBJECTIVE: To investigate factors associated with the successful recruitment of general practices to a randomized controlled trial. STUDY DESIGN AND SETTING: Analysis of accrual of primary care centers to a randomized controlled trial in the UK. RESULTS: Those practices promptly agreeing to take part had better target achievement and a higher proportion of white British residents locally. Participating practices had a mean Quality and Outcomes Framework attainment of 92% of the points available, whereas nonparticipating practices achieved 88% (P=0.009). Participating practices were located in areas with a higher proportion of white British residents (mean 89%), in comparison to nonparticipating practices (mean 84%, P=0.004). Reasons given by practices to explain nonparticipation were primarily related to internal factors, with 38% of practices approached saying that they could not participate for such reasons. CONCLUSION: There are some small differences between participating practices and nonparticipants in achievement of government targets and in the local ethnic mix. The primary reason given by practices for nonparticipation was workload or time pressures, with over a third of practices reporting being prevented by issues relating to practice organization. It may be that practices with workload or organizational difficulties require additional support to participate in research.