A lacunar stroke is a stroke in which one of the arteries supplying blood to the brain is blocked. A randomized, double-blind study was done to see whether recurrence of stroke could be prevented by adding a drug (clopidogrel) to the usual regimen of aspirin. The total sample size was 3020; assume exactly half were randomly assigned to aspirin alone, and half were assigned to the drug plus aspirin. There were 125 strokes in the aspirin-plus-drug group and 138 strokes in the aspirin-alone group.
a. Was this an observational study or controlled experiment? Explain.
b. Which sample did better, the group on just aspirin or the group on aspirin plus the drug? If you perform a hypothesis test with a two-sided alternative, the p-value is 0.401.
c. Choose the correct conclusion:
i. We have shown that the drug has no effect on the rate of strokes.
ii. We have not shown that the drug affects the rate of strokes.
d. Explain your choice for part c.