Calculate Cohen’s d with the small-sample Hedges correction.
Cohen’s d is biased upward in small samples, which the Hedges correction removes. The two converge as sample sizes grow beyond about 50 per group. Reporting d with its standard error allows a confidence interval on the effect, which is far more informative than a point estimate alone.
Cohen's D
d = (M₁ − M₂) ÷ s_pooled, with s_pooled the sample-size weighted standard deviation
d = (M₁ − M₂) ÷ s_pooled, with s_pooled the sample-size weighted standard deviation Cohen’s d is biased upward in small samples, which the Hedges correction removes. The two converge as sample sizes grow beyond about 50 per group.
Reporting d with its standard error allows a confidence interval on the effect, which is far more informative than a point estimate alone.
This calculator takes 6 inputs: Mean of group 1, Mean of group 2, Standard deviation of group 1, Standard deviation of group 2, Sample size of group 1, Sample size of group 2. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.