Vermont maple sugar producers sponsored a testing program to determine the benefit of a new fertilizer. A random sample of 27 maple trees in Vermont were chosen and treated with one of three levels of fertilizer. In this experimental setup, nine trees

(three in each of three climatic zones) were treated with each fertilizer level and the amount of sap produced (in milliliters) by the trees was measured. The results are as follows.

a. Can you reject the hypothesis of no interactions? Explain.

b. Can the main effect of fertilizer on the amount of sap be interpreted? If so, interpret the main effect, using the α = 0.05 level of significance. If not, explain why not.

c. Can the main effect of climatic zone on the amount of sap be interpreted? If so, interpret the main effect, using the α = 0.05 level of significance. If not, explain why not.

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Low Fertilizer Medium Fertilizer High Fertilizer Southern Zone 76.2 80.4 74.2 88.0 94.1 93.0 84.2 87.5 83.1 Central Zone 81.4 85.9 86.9 98.2 94.7 96.2 90.3 89.9 93.2 Northern Zone 86.5 85.2 80.1 88.4 90.4 92.2 81.4 84.7 82.2