Approximately 85% of patients diagnosed with multiple sclerosis have attacks—often called relapses—of neurologic problems. The relapses are followed by periods during which symptoms improve partially or fully. This form of the disease is called relapsing-remitting multiple sclerosis (RRMS). In a double-blind study, researchers tested whether the drug natalizumab reduces the annual relapse rate for RRMS patients. A total of 942 RRMS patients ages 18 to 50 years, inclusive, were randomly assigned to receive the drug or a placebo by intravenous infusion for 120 weeks. The study concluded that the drug reduces the relapse rate.
a. Describe the treatment and control groups.
b. Is the study an experiment or an observational study? Explain.
c. What does random assignment mean in this study? How could this be accomplished?
d. Describe the sample and the population.