Select the analysis options for test for equal variances

Stat > ANOVA > Test for Equal Variances > Options

Confidence level

Enter a confidence level for the Bonferroni simultaneous confidence intervals. Usually, a simultaneous confidence level of 95% works well.

The simultaneous confidence level is the percentage of times that the entire set of confidence intervals contains the true standard deviations for all group comparisons, if you repeat the study multiple times. A 95% simultaneous confidence level indicates that, if you perform the study 100 times, the entire set of confidence intervals contains the population standard deviations for all groups in 95 of the studies.

For more information, go to Using confidence levels to identify significant differences between factor levels in multiple comparisons and What is the Bonferroni method?.

Use test based on normal distribution

If you know that your data follow a normal distribution, select Use test based on normal distribution to use Bartlett's test rather than the multiple comparisons test and Levene's test. If there are only two groups, Minitab uses the F-test instead of Bartlett's test.

The F-test and Bartlett's test are accurate only for normally distributed data. Any departure from normality can cause these tests to provide inaccurate results. However, if the data follow the normal distribution, the F-test and Bartlett's test are typically more powerful than either the multiple comparisons method or Levene's method.

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