Effect Size Calculator
Calculate Cohen's d and Hedges' g from two group means, standard deviations, and sample sizes.
Cohen's d 0.63
Hedges' g 0.62
Interpretation Medium
Frequently Asked Questions
- For two groups, a common effect size is Cohen's d = (mean1 - mean2) / pooled standard deviation.
- Cohen's d is a standardized difference between two means. It helps show how large the effect is, not just whether it is statistically significant.
- A common rule of thumb is 0.2 small, 0.5 medium, and 0.8 large, though interpretation depends on context.
- Effect size gives magnitude, while a p-value only speaks to evidence against the null hypothesis. Good analysis usually considers both.
- Pooled standard deviation combines variability from both groups into one value, weighted by sample size.
- Hedges' g is a bias-corrected version of Cohen's d that is often preferred for smaller samples.
- Yes. It is useful for experiments, A/B tests, psychology studies, education research, and many other two-group comparisons.
- No. A result can be statistically significant and still have a small effect size, especially in very large samples.