A study was conducted to evaluate the effectiveness of an antihypertensive product. Three groups of 20 rats each were randomly selected from a strain of hypertensive rats. The 20 rats in the first group were treated with a low dose of an antihypertensive product, the second group with a higher dose of the same product, and the third group with an inert control. The amounts of decrease in systolic blood pressure 30 minutes after the rats receive an injection are given in the following table. Note that negative values represent increases in blood pressure.

a. Compare the mean drops in blood pressure for the high-dose group and the control group. Use α = .05 and report the level of significance.
b. Estimate the size of the difference in the mean drops for the high-dose and control groups using a 95% confidence interval.
c. Do the conditions required for the statistical techniques used in parts (a) and (b) appear to be satisfied? Justify your answer.

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