The data displayed below are results from an experiment described in Snedecor and Cochran (1989) on the use of drugs in the treatment of leprosy. The drugs were A and D, which were antibiotics, and F is an inert drug used as a control. The dependent variable Y was a score of leprosy bacilli measured on each patient after several months of treatment. The covariate X was a pretreatment score of leprosy bacilli.

Drugs AD F XY X Y X Y 11 6 6 0 16 13 8 0 6 2 13 10 5 2 7 3 11 18 14 8 8 1 9 5 19 11 18 18 21 23 6 4 8 4 16 12 10 13 19 14 12 5 6 1 8 9 12 16 11 8 5 1 7 1 3 0 15 9 12 20

a. Use proc glm and the one-way covariance (equal slopes) model to analyze this data. Construct an adjusted ANOVA table.

b. Using the above ANOVA table, test the hypothesis H0 : μ1 = μ2 =

μ3 (use the p-value and state decision).

c. Construct 95% confidence intervals for all differences in pairs of means (e.g., μ1 − μ2) adjusted for multiple testing using the Bonferroni method.

d. What does the test of H0 : β = 0 tell you? Test this hypothesis using the above adjusted ANOVA table and state your conclusion.

e. Construct an analysis of variance that is not adjusted for the prescore. What conclusion can you draw from this ANOVA table.