Chantix is a prescription pill used to help smokers who want to quit. However, some doctors are concerned about the potential negative side effects of the drug including nausea, abnormal dreams, insomnia, and headache. A study of the safety and effectiveness of Chantix included 1,493 smokers wanting to quit who volunteered to participate in a clinical trial of the drug. Of the 751 smokers randomly assigned to take Chantix over a 24-week period, 28 experienced serious side effects. Of the 742 smokers randomly assigned to take a placebo over the same period, 16 experienced serious side effects. Researchers were interested in whether the data provide convincing statistical evidence that taking Chantix would increase the risk of serious side effects among all smokers similar to the volunteers. 1. Does this study represent an experiment or observational study?
2. Define the explanatory and response variables.
3. What is the unknown parameter of interest in this study?