An analysis of variance (ANOVA) indicates whether several means come from the same population. Such a procedure is called an omnibus test, because it tests the whole set of means at once (omnibus means “for all” in Latin). In an ANOVA omnibus test, a significant result indicates that at least two groups differ from each other, but it does not identify the groups that differ. So an ANOVA is generally followed by an analysis whose goal is to identify the pattern of differences in the results. This analysis is often performed by evaluating all the pairs of means to decide which ones show a significant difference. In a general framework, this approach, which is called a pairwise comparison, is a specific case of an “a ...
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