Statistical notes for clinical researchers: Sample size calculation 3. Comparison of several means using one-way ANOVA

In this third article about sample size determination, we will discuss sample size determination procedure for comparison of several means. Usually analysis of such data is performed using the analysis of variance (ANOVA) procedure. Because of the complex nature that more than two group means are compared, various types of effect sizes have been suggested including Cohen's f, Eta squared (η2), Partial Eta squared (ηp2), and Omega squared (ω2). Therefore, we will discuss sample size determination procedure using Cohen's f and then will explore various types of effect sizes for ANOVA and their interchangeability.