6. An experiment was conducted to compare the effects of four different drugs (A, B, C, and D) in delaying atrophy of denervated muscles. A certain leg muscle in each of 48 rats was deprived of its nerve supply by surgical severing of the appropriate nerves. The rats were then put randomly into four groups, and each group was assigned treat- ment with one of the drugs. After 12 days, four rats from each group were sacrificed, and the weight W(in grams) of the denervated muscle was obtained for each rat, as listed in the following table. Theoretically, atrophy should be measured as the loss in weight of the muscle, but the initial weight of the muscle could not have been obtained without sacrificing the rat. Consequently, the initial total body weight X (in grams) of the rat was measured. It was assumed that this figure is closely related to the initial weight of the leg muscle. Drugs A and C were large and small dosages, respectively, of atropine sulfate. Drug B was quinidine sulfate. Drug D acted as a control; it was simply a saline solu- tion and could not have had any effect on atrophy. Use ANACOVA to compare the effects of the four drugs, controlling for initial total body weight (X). Use the results given in the SAS output shown next to perform your analysis. (Note: X = 226.125). Drug A Drug B Drug C Drug D (Z1 = 1, (Z2 = 1, (23 = 1, (Z1 = Z2 = Z2 = Z3 = 0) Z1 = Z3 = 0) Z1 = Z2 = 0) Z3 = 0) X W X W X W X W 198 0.34 233 0.41 204 0.57 186 0.81 175 0.43 250 0.87 234 0.80 286 1.01 199 0.41 289 0.91 211 0.69 245 0.97 224 0.48 255 0.87 214 0.84 215 0.87Edited SAS Output (PROC REG) for Problem 6 Regression of W on X, Z1, Z2, and Z3 ANALYSIS OF VARIANCE Sum of Mean Source DF Squares Square F Value Pr > F Model 0.61847 0.15462 10.71 0.0009 Error 1 1 0.15873 0.01443 Corrected Total 15 0.77720 Root MSE 0. 12013 R-Square 0.7958 Dependent Mean 0.70500 Adj R-Sq 0.7215 Coeff Var 17.03922 PARAMETER ESTIMATES Parameter Standard Variable DF Estimate Error t Value Pr > It] Type I SS Intercept 0.17283 0.30373 0.57 0.5808 7.95240 X 0.00319 0.00128 2.49 0.0299 0.32015 Z1 -0.39170 0.09541 -4.11 0.0017 0.20177 Z2 -0.22565 0.09020 -2.50 0.0294 0.06236 Z3 -0. 13505 0.08776 -1.54 0.1521 0.03418