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

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.