Researchers Havar Brendryen and Pal Kraft conducted a study in
Researchers Havar Brendryen and Pal Kraft conducted a study in which 396 subjects were randomly assigned to either an experimental smoking cessation program or control group. The experimental program consisted of the Internet and phone-based Happy Ending Intervention, which lasted 54 weeks and consisted of more than 400 contacts by e-mail, Web pages, interactive voice response, and short message service (SMS) technology. The control group received a self-help booklet. Both groups were offered free nicotine replacement therapy. Abstinence was deﬁned as “not even a puff of smoke, for the last 7 days,” and assessed by means of Internet surveys or telephone interviews. The response variable was abstinence after 12 months. Of the participants in the experimental program, 22.3% reported abstinence; of the participants in the control group, 13.1% reported abstinence.
(a) What type of experimental design is this?
(b) What is the treatment? How many levels does it have?
(c) What is the response variable?
(d) What are the statistics reported by the authors?
(e) According toWikipedia.com,an odds ratio is the ratio of the odds of an event occurring in one group to the odds of it occurring in another group.These groups might be men and women, an experimental group and a control group, or any other dichotomous classiﬁcation. If the probabilities of the event in each of the groups are p (ﬁrst group) and q (second group), then the odds ratio is
An odds ratio of 1 indicates that the condition or event under study is equally likely in both groups.An odds ratio greater than 1 indicates that the condition or event is more likely in the ﬁrst group. And an odds ratio less than 1 indicates that the condition or event is less likely in the ﬁrst group.The odds ratio must be greater than or equal to zero.As the odds of the ﬁrst group approach zero,the odds ratio approaches zero.As the odds of the second group approach zero, the odds ratio approaches positive inﬁnity.Verify that the odds ratio for this study is 1.90.What does this mean?
(f) The authors of the study reported a 95% conﬁdence interval for the odds ratio to be lower bound: 1.12 and upper bound 3.26. Interpret this result.
(g) Write a conclusion that generalizes the results of this study to the population of all smokers.
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