Omega² tamanho efeito
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
About this calculator
The Omega² calculator is an effect size measure used in ANOVA to determine the proportion of variance explained by an independent variable. Unlike Eta², Omega² adjusts for the number of groups and sample size, providing a more accurate estimate. The formula incorporates between-group sum of squares (SSB), degrees of freedom (df), within-group mean squares (MSW), and total sum of squares (SST).
This metric is valuable in scientific experiments to assess the practical significance of observed differences. For instance, in drug efficacy studies, Omega² quantifies whether variations across groups are meaningful. A value near zero suggests the factor does not contribute to data variability.
Interpret Omega² cautiously, as it does not imply causation. Positive values indicate explained variance, but effect size depends on context. Compare results with field-specific benchmarks, such as Cohen's scale (0.01 = small, 0.06 = medium, 0.14 = large) in social sciences.
Frequently asked questions
How does Omega² differ from Eta²?
Omega² adjusts for group count and sample size, while Eta² overestimates by ignoring random variation. Omega² is more conservative.
What is the valid range of Omega² values?
Omega² ranges from -1 (no explained variance) to 1 (all variance explained). Negative values indicate a worse model than chance.
When to use Omega² instead of Eta²?
Use Omega² with more than two groups and when precise statistical adjustment is needed. Eta² is suitable for quick comparisons but less rigorous.
How to interpret an Omega² of 0.08?
According to common benchmarks, 0.08 is considered a medium effect in social sciences, though it may vary by field.