14.34 Diet and weight gain A randomized experiment4 measured weight gain (in grams) of male rats under six diets varying by source of protein (beef, cereal, pork) and level of protein

(high, low). Ten rats were assigned to each diet. The data are shown in the table that follows and are also available in the Protein and Weight Gain data file on the book’s website.

a. Conduct a two-way ANOVA that assumes a lack of interaction.

Report the F test statistic and the P-value for testing the effect of the protein level. Interpret.

b. Now conduct a two-way ANOVA that also considers potential interaction. Report the hypotheses, test statistic, and P-value for a test of no interaction. What do you conclude at the 0.05 significance level? Explain.

c. Refer to part

b. Allowing interaction, construct a 95%

confidence interval to compare the mean weight gain for the two protein levels, for the beef source of protein.

Weight gain by source of protein and by level of protein High Protein Low Protein Beef 73, 102, 118, 104, 81, 107, 100, 87, 117, 111 90, 76, 90, 64, 86, 51, 72, 90, 95, 78 Cereal 98, 74, 56, 111, 95, 88, 82, 77, 86, 92 107, 95, 97, 80, 98, 74, 74, 67, 89, 58 Pork 94, 79, 96, 98, 102, 102, 108, 91, 120, 105 49, 82, 73, 86, 81, 97, 106, 70, 61, 82