t-Test Effect Size (Cohen's d) Formula

Below you will find descriptions and details for the formula that is used to compute Cohen's d effect sizes for t-tests.

Effect size for a t-test (Cohen's d):

Variable definitions:
x₁ and x₂ = the means of group 1 and group 2
σ₁² and σ₂² = the variances of group 1 and group 2