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Industrial Statistics with Minitab by Xavier Tort-Martorell Llabres, Lluis Marco Almagro, Pere Grima Cintas

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11.4 Test for Homogeneity of Variances

Consider again the data on the comparison of phenol contents of different tree varieties. Can we affirm that there is a significant difference among the three varieties of trees with respect to the variability of phenol contents?

Stat > ANOVA > Test for Equal Variances.

nc11uf015.eps

The test results are summarized in the following graph:

nc11uf016.eps

The confidence intervals greatly overlap and the p-values of both tests are large. Therefore, it cannot be stated that the variability is different among the three varieties of trees.

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