Suppose you are interested in determining whether the advice given by a physician during a routine physical examination is effective in encouraging patients to stop smoking. In a study of current smokers, one group of patients was given a brief talk about the hazards of smoking and was encouraged to quit [244]. A second group received no advice pertaining to smoking. All patients were given a follow-up examination. In the sample of 114 patients who had received the advice, 11 reported that they had quit smoking. In the sample of 96 patients who had not, 7 had quit smoking.

(a) Estimate and Interpret the true difference in population proportions p - P2-

(b) Use a statistical package to construct a 95% confidence interval for this difference.

(c) At the 0.

05 level of significance, test the null hypothesis that the proportions of patients who quit smoking are identical for those who received advice and those who did not.

(d) Do you believe that the advice given by physicians is effective? Why or why not?