Consider the data from a study reported by Varma and Chilton (1974), that was later reanalyzed by Jones (1980).

This was a simple crossover dental study comparing a test compound to a placebo with regard to their eect on dental hygiene as measured by the change in a dental hygiene index. There were 34 patients randomized to the rst group and 30 patients randomized to the second group.

(a) Use the Anova function in the car package to analyze the data from this experiment.

(b) Is there a dierence of the test compound and placebo with respect to their eect on dental hygiene? If so, which produces the larger change in the index?

(c) Is there any evidence of a carryover eect of the test compound?

Group 1 Group 2 Subject Period 1 Period 2 Period 1 Period 2 Placebo Test Test Placebo 1 0.83 1.83 1.67 0.33 2 1.00 2.17 2.50 0.50 3 0.67 1.67 1.00 -0.17 4 0.50 1.50 1.67 0.50 5 0.50 2.33 1.83 0.50 6 0.83 1.83 0.50 0.33 7 1.00 0.50 1.33 0.67 8 0.67 0.33 1.33 0.00 9 0.67 0.50 0.50 0.17 10 0.33 0.67 2.17 0.83 11 0.00 0.83 1.67 0.33 12 1.17 1.33 1.50 0.00 13 0.00 0.67 1.33 0.50 14 0.50 1.83 1.50 0.50 15 0.33 1.50 1.33 0.00 16 0.33 1.50 0.67 -0.17 17 0.50 1.17 1.67 0.50 18 1.00 1.67 2.50 0.67 19 0.00 1.33 1.83 0.00 20 0.50 1.50 0.83 0.67 21 -0.50 2.83 2.33 0.17 22 0.17 2.33 1.17 0.50 23 1.00 1.33 1.33 0.00 24 1.00 1.67 1.33 0.83 25 1.33 0.67 0.33 1.33 26 0.33 0.83 2.17 1.17 27 2.00 1.00 1.00 0.33 28 4.00 0.17 0.33 1.00 29 0.83 1.67 1.17 0.17 30 0.50 1.33 0.50 0.50 31 0.50 1.50 32 0.50 1.67 33 2.17 1.33 34 0.67 1.17