Likely impacts of recruitment site and methodology on characteristics of enrolled patient population: irritable bowel syndrome clinical trial design

Approximately 15–20% of the general population of many western countries fulfill clinical diagnostic criteria for irritable bowel syndrome (IBS) and nearly 50% of referrals and follow-up appointments in hospital gastroenterology clinics are for functional bowel disorders. IBS is a common problem in the community, in primary care (general practice) and in secondary care (hospital, usually ambulatory) settings, and is also seen in tertiary (referral) centers, providing at least four potential settings for recruitment of patients into clinical trials. However, little is known about the influences that cause patients to choose different health-care settings or to stay away from the health-care system as “nonconsulters.” Also, it is not known if patients seen at different health-care settings differ from each other. The aim of this review is to address the following questions: To what extent do subjects identified and enrolled in these settings differ from each other? What is the likely impact of different recruitment methods on subject selection? What problems for the interpretation and generalizability of data from clinical trials might these differences pose? What is the role of the sociomedical context (cultural beliefs and values and the structure of the health-care system) in different countries on the interpretation of clinical studies?