The Physicians Health Study followed 22,000 male physicians for a period of several years. About 11.000 took an aspirin every second day while the rest took a placebo. At the completion of the study, it was noted whether a subject had experienced a heart attack during the period of the study. It was found that the aspirin group had significantly fewer heart attacks than the placebo group. 1 . The factor in the experiment is a. the severity of the heart attack. b. use of a placebo. c. medication used (aspirin or placebo}. d. the length of the study. 2. The response variable in this experiment is a. whether a heart attack occurred. b. the placebo eifect. c. whether the symptoms lessened. d. the iength of the interview