PCORI does not require a minimum project sample size, as this will be up to the investigative team and will vary depending on the specific project. However, as noted in the PFA, "The studies must be relatively large, in part to be able to demonstrate differences in comparative effectiveness in the study arms as randomized, but also to allow adequate power to detect the potential differences in treatment responses in patient subgroups." We note that estimating sample size sufficient to provide adequate power for subgroup analysis can be challenging and typically requires expert consultation. Other potential challenges to achieving target sample size (e.g., unintended crossover) should also be factored into sample size considerations as appropriate.
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