Participant Recruitment, Screening, and Enrollment

Participant recruitment and retention are key success factors in a clinical trial. Failure to enroll the required number of participants in a timely manner can have significant impact on trial budget and timelines, and data gaps due to under-recruitment or early dropout of participants may lead to misinterpretation or unreliability of trial results. Prior to the start of a trial, a thorough recruitment plan should be set up, considering the screen failure rate, the potential need to replace early dropouts, and the geographical distribution of participants, timelines, and budgetary constraints. Understanding how to calculate the recruitment rate based on the number of enrolled participants per site per month will help in assessing the probability of successful recruitment. In addition, recruitment planning tools and services such as comparison with benchmarking data from analogous historical or ongoing trials, simulation tools, and specialist service agencies may support the setup of a robust recruitment plan. Risk factors with the potential of leading to under-recruitment, over-recruitment, or recruitment of unsuitable participants should be identified upfront to allow risk mitigation as far as possible, e.g., through protocol amendments or increasing the number of participating centers. Evaluation of the most appropriate channels to identify and contact trial candidates will ensure optimal turnout in relation to the financial and resource investments. Strategies for participant screening, enrollment, and retention are reviewed in this chapter.