Tehran University of Medical Sciences Frontiers in Emergency Medicine 2717-3593 4 1 2019 11 27 e15 e15 Ahmed Negida Faculty of Medicine, Zagazig University, Zagazig, El-Sharkia, Egypt 2019 11 27 In the previous educational articles, we explained how to calculate the sample size for a rate or a single proportion, for an independent cohort study, for an independent case-control study, for a diagnostic test accuracy study, and for a superiority clinical trial. In this article, we will explain how to calculate the sample size for a non-inferiority or equivalence clinical trial. https://fem.tums.ac.ir/index.php/fem/article/view/302 https://fem.tums.ac.ir/index.php/fem/article/download/302/245