Read the portion of the abstract of a scientific study that appears below, and then answer the questions that follow.
"Methods: In this . . . double-blind, placebo-controlled . . . study, 611 patients were randomly assigned, in a 4:4:1 ratio, to [receive] 5 mg of tofacitinib twice daily, 10 mg of tofacitinib twice daily, or placebo. The primary end point, assessed at month 3, was the percentage of patients with at least a 20% improvement on the American College of Rheumatology scale (ACR 20), Results: At month 3, a higher percentage of patients in the tofacitinib groups than in the placebo groups met the criteria for an ACR 20 response (59.8% in the 5-mg tofacitinib group and 65.7% in the 10-mg tofacitinib group vs. 26.7% in the placebo group, P 6 0.001 for both comparisons)."
a. Identify the treatment variable and the response variable.
b. Was this a controlled experiment or an observational study? Explain.
c. Do the sample percentages suggest that the drug was effective in achieving a 20% reduction in symptoms?
d. What does the small p-value show?
e. Can you conclude that the use of tofacitinib increases the chances of a 20% improvement in symptoms? Why or why not?