A large group of randomly selected people in the UM health system were divided into three groups and instructed to take a two-hour reasoning exam. Before the test, Group 1 was administered a cognition-enhancing stimulant, Group 2 was administered a placebo, and Group 3 was given nothing. Group 1 and Group 2 performed similarly, and both groups performed statistically significantly better than Group 3. What should you say about (a) whether or not regression to the mean is relevant to understanding this result (b) the possible role of placebo effect for each group (c) whether you have reason to think that the stimulant is effective