How this calculator works
Cohen d standardises the group-1 minus group-2 mean difference by a pooled sample SD. Hedges g applies the exact gamma-function correction for small samples. Glass delta uses group 2 as the reference SD. The t conversion assumes a pooled-variance independent-groups t test; it is not a paired or Welch conversion. Correlation mode returns r and r² without forcing them into a mean-difference measure.
Formula
s_p² = [(n1-1)s1²+(n2-1)s2²]/(n1+n2-2); d = (mean1-mean2)/s_p; g = J(df)d; J(df) = Γ(df/2)/(√(df/2)Γ((df-1)/2)); d = t√(1/n1+1/n2).
Worked example
With means 12 and 10, both SDs 2 and both sample sizes 10, pooled SD is 2, d is 1 and exact Hedges g is about 0.9576464.
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Frequently asked questions
Does a large effect prove causality?
No. Study design, confounding and uncertainty still matter.
What does the sign mean?
For group summaries, positive means group 1 has the higher mean. Reversing group order reverses the sign.
Can I use universal small, medium and large labels?
Such labels are rough conventions. Interpret the size against real outcomes and relevant prior studies.