Which option would be an example of a primary endpoint in a clinical trial?

• A. Adverse event rate.
• B. Enrollment rate.
• C. Time to completion.
• D. Main outcome used to evaluate treatment effect.

Answer: (D)

The main concept being tested is that the primary endpoint is the main efficacy outcome a trial is designed to measure to determine if the treatment works. It is the central question the study aims to answer and is used in planning the study, including sample size, to reflect the treatment’s effect. The option described as the main outcome used to evaluate treatment effect fits this perfectly, because it directly names the principal measure of efficacy the trial is designed around and powered to detect. Adverse event rate relates to safety and tolerability, and is typically a secondary or safety endpoint rather than the main measure of treatment effect. Enrollment rate concerns recruitment, not the treatment’s impact on disease or condition. Time to completion is a logistics or duration-related metric and, unless specifically chosen as the efficacy measure in a time-to-event design, does not represent the primary endpoint.