Nicotine patches are often used to help smokers quit. Does giving medicine to fight depression also help? A randomized double-blind experiment assigned 244 smokers to receive nicotine patches and another 245 to receive both a patch and the antidepressant drug bupropion. After a year, 40 subjects in the nicotine patch group had abstained from smoking, as had 87 in the patch-plus-drug group. Your task is to construct and interpret a 99% confidence interval for the difference in the proportion of smokers who abstain when using bupropion and a nicotine patch and the proportion who abstain when using only a patch.