Question: 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 attack. 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. Is this an observation al study or experimented?” Why? What are the explanatory variables?