The following data come from a study that examines the effic

The following data come from a study that examines the efficacy of saliva cotinine as an indicator for exposure to tobacco smoke. In one part of the study, seven subjects - none of whom were heavy smokers and all of the whom has abstained from smoking for at least one week prior to the study - were each required to smoke a single cigarette. Samples of saliva were taken from all individuals 2, 12, 24, and 48 hours after smoking the cigarette. The cotinine levels at 12 hours and at 24 hours are shown below.

Subject

Cotinine levels (nmol/l)

After 12 Hours

After 24 Hours

1

2

3

4

5

6

7

73

58

67

93

33

18

147

24

27

49

59

0

11

43

Let µ₁₂ represent the population mean cotinine level 12 hours after smoking the cigarette and µ₂₄ the mean cotinine level 24 hours after smoking. It is believed that µ₂₄ must be lower than µ₁₂.

(a) Construct a one-sided 95% confidence interval for the truth difference in population mean µ₁₂ - µ₂₄.

(b) Test the null hypothesis that the population means are identical at the ? = 0.05 level of significance. What do you conclude?

Note:

Solution