Role of Effect Sizes in Contemporary Research in Counseling

Effect sizes (e.g., Cohen's d, Glass's Δ, η², adjusted R², ω²) quantify the extent to which sample results diverge from the expectations specified in the null hypothesis. The present article addresses 5 related questions. First, is the advocacy for reporting and interpreting effect sizes part of the controversy over statistical significance testing? Second, why cannot p values be used as effect sizes? Third, what are the various categories of effect sizes and some commonly used examples of each type? Fourth, how should effect sizes be interpreted? Fifth, what are some recommendations for further reading?