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Effect Size Calculator

Find Cohen's d effect size between two groups.

Cohen's d 0.6

Formula: d = (mean₁ − mean₂) ÷ pooled SD

Step-by-step with your numbers:
1. Values used:
2. Mean 1 = 78
3. Mean 2 = 72
4. Pooled standard deviation = 10
5.
6. Cohen's d = 0.6
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Effect size measures how big a difference is, independent of sample size.

The math behind it

Cohen's d = (mean difference) ÷ pooled SD. Rough guide: 0.2 small, 0.5 medium, 0.8 large.

Worked example

Means 78 vs 72, pooled SD 10 → d = 0.6 (medium).

FAQ

Why report effect size?

A result can be statistically significant yet trivially small; effect size shows practical importance.

Related calculators

Cohen's D Calculator Find Cohen's d effect size from two group means and SDs. Pooled Standard Deviation Calculator Combine two sample standard deviations into a pooled estimate. Power Analysis Calculator Estimate statistical power for a one-sample test.