Effect Size Cohens Calculator Guide
Cohen’s d (Effect Size)
Cohen’s d measures the standardized difference between two means.
Formula
d = (x̄₁ − x̄₂) / s_p
where s_p is the pooled standard deviation.
Example
Means 55 and 50, pooled SD 8 → d = (55 − 50)/8 = 0.625.
FAQs
Interpretation?
Small ≈ 0.2, medium ≈ 0.5, large ≈ 0.8 (rules of thumb).
Unequal variances?
Consider Hedges’ g or Glass’s Δ.