RESUMEN
Little is known about how barriers to research participation are perceived, affected by or interact with patient characteristics, or how they vary over the course of a clinical trial. Participants (285) in the Renin-Angiotensin System Study (RASS), a randomized clinical primary prevention study of diabetic nephropathy and retinopathy at 2 Canadian and 1 US university, rated potential barriers to research participation yearly for 5 years. Baseline barriers rated as most adversely affecting participation were: missing work; frequency of appointments and procedures; study length; number of appointments and procedures; access to study location; and physical discomfort associated with procedures. Inadequate social support, unstable job, and the use of alcohol and drugs were cited relatively infrequently, suggesting that although they may be important, candidates for whom these might be issues likely self-selected out of the study. Gender and gender by age interactions were found for specific perceived barriers, such as work and child care, and baseline barriers correlated with adherence. Elucidating the natural history of barriers to research participation is a step toward identifying strategies for helping participants overcome them, and ultimately may enhance the conduct of research.