Tamanho efeito Cohen d
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
d = (M₁-M₂)/s_pooled
About this calculator
The Cohen's d effect size calculator quantifies the difference between two group means in standard deviation units, enabling cross-study comparisons. It uses the formula d = (M₁ - M₂)/s_pooled, where s_pooled is the combined standard deviation of both groups. This standardization helps interpret differences independent of original measurement scales.
This metric is widely used in scientific research and A/B testing to assess practical significance. For example, it can compare medication efficacy or marketing strategies. Common thresholds: d = 0.2 (small), 0.5 (medium), 0.8 (large) per Cohen's guidelines. Values above 0.8 suggest substantial effects.
Key assumptions: normal distribution and equal variances. For unequal group sizes, the pooled standard deviation adjusts automatically. Note that effect size differs from statistical significance, small d values may indicate negligible real-world impact even with statistically significant results.
Frequently asked questions
What is Cohen's d effect size?
It's a standardized measure of the difference between two means, expressed in standard deviation units. It shows how much groups differ in universal statistical terms.
How does the calculator compute the pooled standard deviation?
It combines the standard deviations of both groups, weighted by sample sizes. Formula: s_pooled = √[(s₁²(n₁-1)+s₂²(n₂-1))/(n₁+n₂-2)].
When to use Cohen's d instead of a t-test?
Use d to interpret effect magnitude while t-tests assess statistical significance. Cohen's d reveals practical importance beyond p-values.
What are critical values for interpreting d?
Typical thresholds: d = 0.2 (small), 0.5 (medium), 0.8 (large). These are general guidelines that vary by field of study.
How does the calculator handle unequal group sizes?
The formula automatically adjusts the pooled standard deviation using sample weights for accurate effect size calculation.