Effect Size Measures

Abstract

Abstract A variety of measures of effect magnitude are described. Many of the measures can be classified as either measures of effect size (typically, standardized mean differences) or measures of strength of association. There also is a large group of statistics that do not fit into either category. Measures of effect magnitude are used for a variety of purposes: (a) to estimate the sample size required to achieve an acceptable power, (b) to integrate the results of empirical research studies in meta‐analyses, (c) to supplement the information provided by null hypothesis significance tests, and (d) to determine whether research results are practically significant.