How do inclusion and exclusion criteria affect recruitment speed and study duration?
Inclusion and exclusion criteria are one of the key elements of clinical trial design. Although they are often viewed primarily as a tool to ensure population homogeneity and patient safety, in practice they have a direct impact on recruitment speed, the risk of delays, and the overall duration of a study.
Overly restrictive inclusion criteria significantly narrow the pool of potential participants. Even in centers with a large patient population, seemingly minor nuances—such as narrow laboratory value ranges, short wash-out periods, or extensive lists of exclusionary comorbidities—can lead to high screen failure rates. As a result, the recruitment phase is prolonged, screening costs increase, and the study may require the opening of additional sites or extensions to the project timeline.
On the other hand, criteria that are too broad, while seemingly facilitating faster recruitment, may introduce other risks: increased data variability, challenges in interpreting results, and the need for additional analyses. This, in turn, can extend the statistical analysis phase and delay study completion—or even the regulatory submission process.
The alignment of criteria with real-world clinical practice is also crucial. Criteria that fail to reflect standard treatment pathways, the availability of diagnostic procedures, or the typical patient profile in a given country often lead to operational issues already at the screening stage. Any clarification, protocol amendment, or reinterpretation of criteria during the study translates into additional time, higher costs, and increased workload for study teams.
From a project management perspective, well-designed inclusion and exclusion criteria are a powerful tool for optimizing both timelines and budgets. They enable more accurate predictions of recruitment speed, realistic estimation of the number of patients to be screened, and minimization of downtime risks. Moreover, clearly defined and operationally “readable” criteria reduce the number of sponsor queries, limit ambiguities, and streamline site operations.
In practical business terms, this means one thing: every hour invested in refining criteria at the study planning stage pays off many times over during execution. Optimal criteria lead to faster recruitment, shorter study duration, lower operational costs, and greater overall project predictability. This is why an increasing number of sponsors and CROs view criteria design not merely as a protocol requirement, but as a strategic determinant of clinical trial success.
Not sure whether your planned inclusion and exclusion criteria are well calibrated to achieve your objectives within the expected timelines? Need insight into how quickly sites can realistically recruit patients? Schedule an initial consultation with our experts.
