Challenges in pragmatic trials: selection and inclusion of usual care sites.

This second article in the series on pragmatic trials describes the challenges in selection of sites for pragmatic clinical trials and the impact on validity, precision, and generalizability of the results. The selection of sites is an important factor for the successful execution of a pragmatic trial and impacts the extent to which the results are applicable to future patients in clinical practice. The first step is to define usual care and understand the heterogeneity of sites, patient demographics, disease prevalence and country choice. Next, specific site characteristics are important to consider such as interest in the objectives of the trial, the level of research experience, availability of resources, and the expected number of eligible patients. It can be advisable to support the sites with implementing the trial-related activities and minimize the additional burden that the research imposes on routine clinical practice. Health care providers should be involved in an early phase of protocol development to generate engagement and ensure an appropriate selection of sites with patients who are representative of the future drug users.