One App to Rule Them All: A One-Stop Calculator and Guide for 95 Effect-Size Variants for Two-Group Comparisons of Central Tendency, Variability, Overlap, Dominance, and Distributional Tails

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The prevalence of effect-size (ES) reporting has risen significantly, yet studies comparing two groups tend to rely exclusively on the Cohen’s d family of ESs. In this article, we aim to broaden the readers’ horizon of known ESs by introducing various ES families for two-group comparisons, including indices of standardized differences in central tendency, overlap, dominance, and differences in variability and distributional tails. We describe parametric and nonparametric estimators in each ES family and present an interactive web application (R Shiny) for computing these ESs and facilitating their application. This one-stop calculator allows for the computation of 95 applications of 67 unique ESs and their confidence intervals and various plotting options and provides detailed descriptions for each ES, making it a valuable resource for both self-guided exploration and instructor-led teaching. With this comprehensive guide and its companion app, we aim to improve the clarity and accuracy of ES reporting in research design that involves two-group comparisons.