cohensH

Computes Cohen's h effect size for the difference between two proportions.

Cohen's h measures how far apart two proportions are on a scale that accounts for the non-linear nature of proportions. It applies an arcsine transformation to each proportion before computing the difference, which stabilizes comparisons across the full range from 0 to 1. Values around 0.2, 0.5, and 0.8 are conventionally considered small, medium, and large effects respectively (Cohen, 1988). The sign indicates direction: positive when p1 exceeds p2. The result is bounded between -pi and pi.

Example:

cohensH(p1 = 0.65, p2 = 0.50) // ~0.31 (small-medium effect)
cohensH(p1 = 0.80, p2 = 0.20) // ~1.29 (large effect)
cohensH(p1 = 0.50, p2 = 0.50) // 0.0 (no effect)

Parameters