In the depression and heart attack research described in Exercise R5.17, 32% of the diseased group were smokers, compared with only 23.7% of those free of heart disease.
a) Create a 95% confidence interval for the difference in the proportions of smokers in the two groups.
b) Is this evidence that the two groups in the study were different?
c) Could this be a problem in analyzing the results of the study?

Data From Exercise R5.17

In a study of how depression may affect one’s ability  to survive a heart attack, the researchers reported the ages of  the two groups they examined. The mean age of 2397 patients  without cardiac disease was 69.8 years (SD = 8.7 years), while for the 450 patients with cardiac disease, the mean and standard deviation of the ages were 74.0 and 7.9, respectively.