In a 2018 study reported in The Lancet, a randomized, double-blind controlled experiment was conducted to determine the effect of the drug upadacitinib on patients with active rheumatoid arthritis. Patients were randomly assigned to receive the drug or a placebo. After 12 weeks, patients receiving the drug had significant improvement compared to those receiving the placebo.

a. Identify the treatment and response variables.

b. Restate the conclusion of the study in terms of a cause-and-effect conclusion. Why can a cause-and-effect conclusion be made from this study?