Smoking cessation. Chantix is different from most other quit-smoking products in that it targets nicotine receptors in the brain, attaches to them, and blocks nicotine from reaching them. As part of a larger randomized controlled trial, generally healthy smokers who smoked at least 10 cigarettes per day were assigned at random to take Chantix or a placebo. The study was double-blind, with the response measure being continuous absence from smoking for Weeks 9 through 12 of the study. Of the 352 subjects taking Chantix, 155 abstained from smoking during Weeks 9 through 12, while 61 of the 344 subjects taking the placebo abstained during this same time period.²² Give a 99% confidence interval for the difference (treatment minus placebo) in the proportions of smokers who abstained from smoking during Weeks 9 through 12.