Investigation 3: Nicotine lozenge (assigned Tues Jan 12, due Tues Jan 19)

You may work with one other person on this assignment, handing in one report with both names. Word-processed reports are much preferred to hand-written ones. Please copy/paste relevant, well-labeled Minitab output into a Word file as appropriate.

Helping smokers to quit continues to be a very important and challenging public health goal. In a recent study of the effectiveness of a nicotine lozenge, smokers who wanted to quit were randomly assigned to one of two groups: one group received nicotine lozenges and the other group received placebo lozenges. The subjects were compared on various background variables at the beginning of the study, and at the end of the study they were compared on whether or not they successfully abstained from smoking.

a) Is this an observational study or an experiment? Explain how you can tell.

b) Identify the observational units, explanatory variable, and response variable.

c) Of the 459 subjects in the nicotine group, 42.9% were male. Of the 458 subjects in the placebo group, 40.2% were male. Conduct a significance test of whether these proportions differ significantly at the .05 level. Report the hypotheses, test statistic and p-value. Also summarize your conclusion.

d) Explain why the researchers would be glad for the null hypothesis not to be rejected in the test in c).

e) At the end of the 52-week study, 17.9% of the nicotine group had successfully abstained from smoking, compared to 9.6% of the placebo group. Conduct a z-test whether these data provide strong evidence that the nicotine lozenge is more effective than the placebo lozenge, using the .01 significance level. Report the hypotheses, test statistic and p-value. Also summarize your conclusion.

f) Is it legitimate to draw a cause-and-effect conclusion between the nicotine lozenge and the increased rate of abstaining from smoking? Explain.

g) Produce a 95% confidence interval for the difference in proportions of abstaining from smoking between the two groups. Also interpret this interval.

h) Now consider only the subjects that received nicotine lozenges. Produce a 95% confidence interval to estimate the population proportion who would successfully abstain from smoking for 52 weeks when using the nicotine lozenge. Also interpret this interval.