7.21. A 30-month study evaluated the degree of addiction that teenagers form to nicotine once they begin experimenting with smoking.8 The study used a random sample of 332 seventh-grade students in two Massachusetts cities who had ever used tobacco by the start ofthe study. The response variable was constructed from the Hooked on Nicotine Checklist (HONC). This is a list of ten questions such as "Have you ever tried to quit but couldn't?" The HONC score is the total number of questions to which a student answered yes.

The higher the score, the greater the dependence on nicotine. There were 75 smokers and 257 exsmokers atthe end ofthe study. The HONC means describing nicotine addiction were 5.9 (.9 = 3.3)

for the smokers and 1.0 {s = 2.3) for the exsmokers.

(a) Find and interpret a point estimate to compare HONC means for smokers and ex-smokers.

(b) Software reports a 95% confidence interval of

(4.1,5.7). Interpret.

(c) Was the HONC sample data distribution for ex-smokers approximately normal? How does this affect inference?