Determining the strength of an association between variables following an Analysis of Variance (ANOVA) is often crucial for a thorough understanding of the results. The `rstatix` package in R provides a convenient and streamlined approach to compute effect size, specifically eta squared () and omega squared (), as well as partial eta squared, alongside ANOVAs. For instance, after conducting an ANOVA using `anova_test()` from `rstatix`, the output readily includes these effect size estimates. Moreover, the package allows calculating the correlation coefficient (r) based on the ANOVA results which provides another measure of the effect size. This is achieved by relating the F-statistic, degrees of freedom, and sample size to derive the r value, representing the strength and direction of the linear relationship.
Calculating effect size provides valuable context beyond statistical significance. While a p-value indicates whether an effect likely exists, the magnitude of that effect is quantified by metrics like eta squared, omega squared, and r. This understanding of effect size strengthens the interpretation of research findings and facilitates comparisons across studies. Historically, reporting solely p-values has led to misinterpretations and an overemphasis on statistical significance over practical relevance. Modern statistical practice emphasizes the importance of including effect size measurements to provide a more complete and nuanced picture of research results.