Many studies have found that people who drink alcohol in moderation have lower risk of heart attacks than either nondrinkers or heavy drinkers. Does alcohol consumption also improve survival after a heart attack? One study followed 1913 people who were hospitalized after severe heart attacks. In the year before their heart attacks, 47% of these people did not drink, 36% drank moderately, and 17% drank heavily. After four years, fewer of the moderate drinkers had died. (a) What type of study is this? Observational study: prospective Observational study: retrospective Observational study: cross-sectional Experiment: matched pairs design Experiment: randomized block design Experiment: completely randomized design (b) What population or populations are represented in the study? all individuals who drink alcohol all heavy drinkers and all nondrinkers all individuals who have suffered a severe heart attack all individuals who drink and have been hospitalized (c) What is the explanatory variable? time until a heart attack alcohol consumption level (none, moderate, heavy) number of heart attacks death (yes, no) (d) What is the response variable? time until a heart attack number of heart attacks alcohol consumption level (none, moderate, heavy) death (yes, no)