Effect-size workbench
Calculate pooled standard deviation, Cohen’s d, and small-sample-corrected Hedges’ g for two independent groups.
The result
Method & assumptions
For independent groups and a common population-variance assumption. The Hedges correction is an approximation. Positive values mean group A is higher; they do not automatically mean better. No clinical interpretation or confidence interval is implied.
Sanity check
Example: equal SDs of 3, group means 12 and 10, and 20 observations per group give d≈0.6667 and g≈0.6534.
sp = √[((nA−1)sA² + (nB−1)sB²)/(nA+nB−2)] d = (meanA−meanB)/sp g ≈ [1−3/(4df−1)] × d; df=nA+nB−2
Implementation version 1.0 · 2026-10-15. Deterministic formulas or editorial rules, with no AI model or external service processing your inputs.
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