Default Bayes factors for testing the (in)equality of several population variances

Testing the (in)equality of variances is an important problem in many statistical applications. We develop default Bayes factor tests to assess the (in)equality of two or more population variances, as well as a test for whether a population variance equals a specific value. The resulting test can be used to check assumptions for commonly used procedures such as the t-test or ANOVA, or test substantive hypotheses concerning variances directly. We show that our Bayes factor fulfills a number of desiderata. Researchers may have directed hypotheses such as σ12 > σ22, they may want to extend (Formula presented) to have a null-region, or wish to combine hypotheses about equality with hypotheses about inequality, for example σ12 = σ22 > (σ32, σ42). We extend our Bayes factor test to allow for these deviations from our proposed default and illustrate it on a number of practical examples. Our procedure is implemented in the R package bfvartest.

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