In screening for compounds useful in treating hypertension ( high blood pressure), ­researchers assign six rats to each of three groups. The rats in group 1 receive .1 mg/ kg of a test compound; those in groups 2 and 3 receive .2 and .4 mg/ kg, respectively. The response of interest is the decrease in blood pressure 2 hours postdose compared to the corresponding predose blood pressure. The data are shown here:

a. Fit the following model to the data.

b. Use residual plots to examine the fit to the model in part (a).
c. Conduct a statistical test of H0: β1 ‰¤ 0 versus Ha: β1 > 0. Give the p-value for your test.

Dose,r Blood Pressure Drop, y (in m Hg) Group 1 Group 2 Group 3 1 mg/kg 10 12 15 16 13 11 2 mg/kg 25 22 26 19 8 24 4 mg/kg 30 32 35 27 2629