O'Brien teste variância
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
About this calculator
O'Brien's test is a statistical tool to assess variance homogeneity across groups. It checks whether samples come from populations with equal variances, a key assumption for ANOVA. The formula transforms raw data into an F-like statistic, comparing variability between groups and within them.
The calculator applies a transformation to observed values, reducing outliers' impact and asymmetry. It then computes the F statistic and compares it to a critical value to reject the null hypothesis of equal variances. The result indicates if variance differences are statistically significant.
This test is suitable when non-random variations between groups are suspected, especially in studies with unbalanced samples or mildly non-normal distributions. Caution: the test is sensitive to extreme values, and small samples may lower accuracy. Always check data normality before applying it.
Practical example: if a study compares three drugs' effectiveness at different doses and group standard deviations vary widely, the calculator helps determine if these differences invalidate total variation analysis.
Frequently asked questions
Why check variance homogeneity?
Many statistical tests, like ANOVA, require similar variances across groups. Significant differences can invalidate results.
How does the calculator transform data?
It applies a formula that reduces outliers' influence, ensuring a balanced comparison between groups.
What if the test rejects the null hypothesis?
Consider alternatives like Welch ANOVA or data transformations to stabilize variances.
Is the test affected by sampling?
Yes, very small or unbalanced samples may lower accuracy. Recommend at least 10 observations per group.
Can I use this test with categorical data?
No, O'Brien's test requires continuous variables. Use chi-square or Fisher's tests for categorical data.