Refer to Exercise 10.23 about studying nicotine dependence using a random sample of teenagers. Of those seventh graders in the study who had tried tobacco, the mean HONC score was 2.8 (s = 3.6) for the 150 females and 1.6 (s = 2.9) for the 182 males.
a. Find a standard error for comparing the sample means. Interpret.
b. Find the test statistic and P-value for H₀: μ₁= μ₂ against H_a: μ₁‰  μ₂. Interpret and explain what (if any) effect gender has on the mean HONC score.
c. Do you think that the HONC scores were approximately normal for each gender? Why or why not? How does this affect the validity of the analysis in part b?

Previous exercise

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, €œHave you ever tried to quit but couldn€™t?€ and €œIs 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.

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