The Journal of the American Medical Association

(Apr. 21, 1993) reported on the results of a National Health Interview Survey designed to determine the prevalence of smoking among U.S. adults. More than 40,000 adults responded to questions such as "Have you smoked at least 100 cigarettes in your lifetime?" and

"Do you smoke cigarettes now?" Current smokers

(more than 11,000 adults in the survey) were also asked:

"On the average, how many cigarettes do you now smoke a day?" The results yielded a mean of 20.0 cigarettes per day with an associated 95% confidence interval of (1 9.7,20.3).

a. Carefully describe the population from which the sample was drawn.

b. Interpret the 95% confidence interval.

c. State any assumptions about the target populatio~i ol current cigarette smokers that must be satisfied for -

inferences derived from the interval to be valid. I

d. A tobacco industry researcher claims that the mean ;

number of cigarettes smoked per day by regular cigarette smokers is less than 15. Comment on this claim.