Reporting Effect Sizes in Original Psychological Research: A Discussion and Tutorial

Abstract

Statistical practice in psychological science is undergoing reform which is reflected in part by strong recommendations for reporting and interpreting effect sizes and their confidence intervals. We present principles and recommendations for research reporting and emphasize the variety of ways effect sizes can be reported. Additionally, we emphasize interpreting and reporting unstandardized effect sizes because of common misconceptions regarding standardized effect sizes which we elucidate. Effect sizes should directly answer their motivating research questions, be comprehensible to the average reader, and be based on meaningful metrics of their constituent variables. We illustrate our recommendations with empirical examples involving a One-way ANOVA, a categorical variable analysis, an interaction effect in linear regression, and a simple mediation model, emphasizing the interpretation of effect sizes.