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Unformatted text preview: 13.4 Inferences about the comparison of 2 variances • Variance can be used to address problems where we need to compare the consistency of two production processes or to compare the risk of two sets of investments. • When we are comparing two variances, it is a little different than comparing means or proportions. First of all, we use a ratio or fraction to show the comparison, rather than a difference . • So, our hypotheses look like this: 2 2 2 1 * s s F = This has an F distribution, so we now need to use a different table, the F table. The distribution of the statistic is not symmetric like the t and Z are. It is similar to the χ 2 distribution in that it is not negative and is skewed right. Our test statistic is: 2 1 2 2 2 1 2 2 : 1 : 1 a H H σ σ σ σ = • Once again, we have to be clear about labeling our groups. • The tables in the back of the book only show the right-tail of the rejection region. So we have to find the left-tail a little differently than we have before. we have before....
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