10.23 Nicotine dependence A study on nicotine dependence for teenage smokers obtained a random sample of seventh graders. The response variable was constructed from a questionnaire called the Hooked on Nicotine Checklist

(HONC). This is a list of ten questions such as, “Have you ever tried to quit but couldn’t?” and “Is it hard to keep from smoking in places where it is banned, like school?”

The HONC score is the total number of questions to which a student answered yes, so each student’s HONC score falls between 0 and 10. The higher the score, the more hooked that student is on nicotine. One explanatory variable considered in the study was whether a subject reported inhaling when smoking. The following table reports descriptive statistics.

HONC Score Group Students Mean Standard Deviation Inhalers 237 2.9 3.6 Noninhalers 95 0.1 0.5

a. Explain why (i) the overwhelming majority of noninhalers must have had HONC scores of 0 and (ii) on average, those who reported inhaling answered yes to nearly three more questions than those who denied inhaling.

b. Might the HONC scores have been approximately normal for each group? Why or why not?

c. Find the standard error for the estimate 1x1 - x22 = 2.8. Interpret.

d. The 95% confidence interval for 1m1 - m22 is (2.3, 3.3).
What can you conclude about the population means for inhalers and noninhalers?