OPDIVA is a drug developed by Brystol-Meyers Squib that is meant to treat metastatic melanoma, which is the worst form of skin cancer. Survival rates for patients with this cancer are 6 to 10 months. Historically, patients with metastatic melanoma were treated with a combination of chemotherapy and dacarbazine. In clinical trials, 418 patients with metastatic melanoma were randomly assigned to either OPDIVO (n = 210) by receiving 3 mg/kg by intravenous infusion every 2 weeks or dacarbazine (n = 208) by receiving 1000 mg>m² by intravenous infusion every 3 weeks. Of the 210 patients in the OPDIVO group, 45 had survived 12 months; of the 208 patients in the dacarbazine group, 22 had survived 12 months.
(a) What type of experimental design is this study?
(b) What is the response variable? Is it qualitative or quantitative?
(c) What is the factor that is controlled and set at various levels? How many levels are there?
(d) Estimate the difference in proportion of patients who had survived 12 months in the OPDIVO group versus the dacarbazine group with 95% confidence. Interpret the interval.