Effect sizes for experimental research

Abstract

Good scientific practice requires that the reporting of the statistical analysis of experiments should include estimates of effect size as well as the results of tests of statistical significance. Good statistical practice requires that effect size estimates be reported along with some indication of their statistical uncertainty, such as a standard error. This article provides a review of effect sizes for experimental research, including expressions for the standard error of each effect size. It focuses on effect sizes for experiments with treatments having a single degree of freedom but also includes effect sizes for treatments with multiple degrees of freedom having either fixed or random effects.

Keywords: Cohen's d; Hedges' g; effect size; intraclass correlation; ω2. η2.