November 2017 ABC’S (Application of Basic Concepts) in Dermatology Research


Sample size calculation 101: Unraveling the concepts behind the numbers

Mara Therese P. Evangelista MD, DPDS and Nick Huber

Because the objective of a clinical trial is to provide reliable evidence of the efficacy and safety of a treatment, a major issue in the design of clinical trials is ensuring we have a sufficient number of patients to provide the required level of evidence. Essentially, we need to have enough subjects in our trial to give a good chance of detecting a clinically important treatment difference if such a difference exists, while being able to reasonably conclude that no such difference exists if our results do not show it. The focus of this article is the sample size calculation for superiority trials. There are different methods in determining the sample size in trials with a non-inferiority design, or those that are randomized by cluster rather than individually. In order to appreciate the basics of sample size requirements for a trial, some understanding of key statistical concepts is essential.