Refer to Exercise 6.37. The researchers also need to obtain precise estimates of the mean difference in systolic blood pressures for people who use the anti-inflammatory drug versus those who do not.
a. Suppose the sample sizes are the same for both groups. What sample size is needed to obtain a 95% confidence interval for the mean difference in systolic blood pressure between the users and nonusers having a width of at most 5 mm Hg.
b. Suppose the user group will have twice as many patients as the placebo group. What sample size is needed to obtain a 95% confidence interval for the mean difference in systolic blood pressures between the users and nonusers having a width of at most 5 mm Hg.
Exercise 6.37
A study is being planned to evaluate the possible side effects of an anti-inflammatory drug. It is suspected that the drug may lead to an elevation in the blood pressure of users of the drug. AÂ preliminary study of two groups of patients, one receiving the drug and the other receiving a placebo, provides the following information on the systolic blood pressure (in mm Hg) of the two groups:
Assume that both groups have systolic blood pressures that have a normal distribution with standard deviations relatively close to the values obtained in the pilot study. Suppose the study plan provides for the same number of patients in the placebo group as in the treatment group. Determine the sample size necessary for an 
 
 .05 t test to have a power of .80 to detect an increase of 5 mm Hg in the blood pressure of the treatment group relative to that of the placebo group.
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