Recruitment, retention, and blinding in clinical trials.

The recruitment and retention of participants and the blinding of participants, health care providers, and data collectors present challenges for clinical trial investigators. This article reviews challenges and alternative strategies associated with these three important clinical trial activities. Common recruiting pitfalls, including low sample size, unfriendly study designs, suboptimal testing locations, and untimely recruitment are discussed together with strategies for overcoming these barriers. The use of active controls, technology-supported visit reminders, and up-front scheduling is recommended to prevent attrition and maximize retention of participants. Blinding is conceptualized as the process of concealing research design elements from key players in the research process. Strategies for blinding participants, health care providers, and data collectors are suggested.