Smoking is a major risk factor for a number of diseases, including strokes. Smoking is particularly dangerous for people who have already had a stroke. One way to help such people to quit smoking is to make drugs that help stop smoking free to stroke patients. Papadakis et al. (2011) investigated the effectiveness of this idea. They randomly divided a sample of stroke patients who smoked into two groups. One group of 12 patients received the normal advice and prescription for anti-smoking drugs, whereas the other group of 13 patients got the same advice and prescription but were also provided the drugs cost-free. After 6 months, 5 members of the cost-free group had quit smoking, while only 2 members of the other (control) group had quit by that time.

a. Calculate the relative risk of smoking for the cost-free program compared with the controls (prescription only).

b. What statistical method could be used to test for a difference between these two groups in the efficacy of the cost-free anti-smoking program?

c. The 95% confidence interval for relative risk for this study ranges from 0.45 to 1.22. In light of this result, what do you think is the greatest weakness of this study?