Having heart surgery later in the day may be safer than having it in the morning. Researchers studied 596 patients, half of whom had undergone open-heart surgery for aortic valve replacement in the morning and half in the aftemoon. They followed their recoveries for 17 months. On almost every measure heart attack during the operation, major adverse cardiac event, acute heart failure, cardiovascular death afternoon surgery produced significantly fewer complications. 1. What is the sample and population of interest in this study? 2 What information about the sample is not given? 3. Does this study provide evidence that a causal relationship exists between the time of the procedure (moming or afternoon) and number of complications from aortic valve replacement? Please explain.