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Bartlett's testfor homogeneity of varianceBartlett's test assesses equality of variances across groups against the alternative hypothesis that variances are unequal for at least two groups. In essence it is comparing the arithmetic mean of your (k) variances, with their geometric mean variance. The test statistic (T) is calculated as below:
The value of the test statistic (T) is compared with the upper critical value of the χ^{2} distribution with k − 1 degrees of freedom at significance level α. Bartlett's test is sensitive to departures from normality, so should not be used on heavily skewed data. This is sometimes used as a justification to use Levene's test, although Levene's test has its own drawbacks.
