How to Report Effect Size in APA Style

APA 7 expects more than a p-value. For every inferential test you should report an effect size — and, where possible, its confidence interval — because the effect size, not the p-value, tells the reader how big the difference actually is.

The right effect size depends on the test: Cohen's d for mean differences, η² (or partial η²) for ANOVA, and r for correlation. This guide shows the formula, the APA sentence, and the interpretation thresholds for each.

Effect size by test

Cohen's d for t-tests

Report the standardized mean difference with its CI, e.g. d = 0.62, 95% CI [0.18, 1.05], and pair it with the descriptive means.

Eta-squared for ANOVA

Give partial η² for each effect; remember thresholds are guidelines, not laws — interpret in the context of your field.

APA sentence templates

Use a consistent pattern: statistic, df, p, then the effect size and CI in brackets, so reviewers can scan results quickly.