Nine experts rated two brands of Colombian coffee in a taste testing experiment. A rating on a 7 point scale (1 = extremely unpleasing, 7 = extremely pleasing) is given for each of four characteristics: taste, aroma, richness, and acidity. The ­following data stored in Coffee contain the ratings accumulated over all four characteristics:

a. At the 0.05 level of significance, is there evidence of a difference in the mean ratings between the two brands?
b. What assumption is necessary about the population distribution in order to perform this test?
c. Determine the p value in (a) and interpret its meaning.
d. Construct and interpret a 95% confidence interval estimate of the difference in the mean ratings between the two brands.

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BRAND EXPERT C.C. S.E. E.G. B.L C.M C.N. G.N R.M. P.V. 24 27 19 24 22 25 26 27 26 26 27 27 27 27