Cohen's d Effect Size
Statistics & ProbabilityCalculate Cohen's d effect size and Hedges' g correction for differences between two group means, classifying practical magnitude (small, medium, large, very large).
Medium effect Ā· pooled SD 14.509
About this calculator
While p-values indicate whether an observed difference is statistically significant, they do not communicate practical real-world magnitude. Cohen's d standardizes the difference between two sample means by pooled standard deviation.
This calculator computes Cohen's d and Hedges' g (an unbiased correction for small sample sizes), categorizing effect size magnitude into standard benchmarks: small (0.2), medium (0.5), large (0.8), and very large (1.2+).
How It Works & Formula
Pooled Standard Deviation s_p = ā[((nā-1)sāĀ² + (nā-1)sāĀ²) / (nā + nā - 2)]. Cohen's d = (xĢā - xĢā) / s_p. Hedges' g applies the small-sample correction factor J = 1 - 3/(4(nā+nā)-9).
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