Sample size adjustment is used to account for what during a trial?

• A. Events or dropouts
• B. Availability of sites
• C. Budget changes
• D. Regulatory feedback

Answer: (A)

In designing a trial, you want enough information to reliably detect a real treatment effect. The amount of information you get depends on how many participants you can evaluate and how many events you observe. Because people may drop out or not experience the primary endpoint as planned, you adjust the planned sample size to compensate for those losses. If you expect some participants to leave or not contribute usable data, you enroll more subjects so that, once dropouts occur, you still have the required number of evaluable participants and events to preserve statistical power.

That’s why the best answer is to account for events or dropouts. Availability of sites, budget changes, or regulatory feedback can affect feasibility or timelines, but they don’t directly determine the sample size needed to maintain power in the analysis.