Which statement best describes the purpose of subject inclusion criteria in a clinical trial?

• A. To determine the total sample size required
• B. To define who may participate based on inclusion criteria
• C. To specify the statistical analysis plan
• D. To set investigators' qualifications

Answer: (B)

Inclusion criteria define who is eligible to participate in a trial by specifying the characteristics participants must have, such as age, disease status or stage, lab values, and prior treatments. This ensures that the study population truly has the condition of interest and can safely receive the intervention, which helps produce reliable, interpretable results and reduces variability.

This purpose is distinct from determining sample size (power calculations), outlining the statistical analysis plan, or setting investigators’ qualifications. By focusing on who may participate based on predefined criteria, inclusion criteria directly shape the eligible participant pool.