A New York times article ( March 12, 2006) described two studies in which subjects who had recently had a heart attack were randomly assigned to one of four treatments:placebo and three different doses of Vitamin B. In each study , after years of study, the differences among the proportions having a heart attack were judged to be not statistically significant. Identify the (a) response variable, (b) explanatory variable, (c) experimental units, (d) treatments, and (e) explain what it means to say the differences "were judged to be not statically significant".