What must be included in the justification for sample size?

• A. Reason for choice of sample size, including reflections on the power of the trial and clinical justification
• B. The sponsor's preferred font for documents
• C. The site travel policy
• D. The pharmacogenomics testing plan

Answer: (A)

When planning a trial, the sample size justification must show why that number of participants is needed to reliably answer the research question. This means linking the chosen size to both statistical power and clinical relevance. You should explain the assumptions used in the power calculation—such as the expected treatment effect to detect (the difference you deem clinically meaningful), the variability or standard deviation, the alpha level (type I error), and the desired power (usually 80% or 90%)—and how anticipated dropouts affect the total enrollment. Importantly, it also ties back to the study’s clinical objectives, showing that enrolling enough participants is essential to detect a meaningful difference without exposing more participants than necessary to the trial. Items like sponsor font preferences, site travel policies, or pharmacogenomics testing plans are administrative or protocol components and do not belong in the sample size justification.