Does regular exercise reduse the risk of a heart attack? Provided are two ways to study this question.
1. A researcher finds 2000 men older than age 40 who exercise regularly and have not had heart attacks. She matches each with a similar man who does not exercise regularly, and she follows both groups for 5 years.
2. Another researcher finds 4000 men older than age 40 who have not had heart attacks and are willing to participate in a study. She assigns 2000 of the men to a regular program of supervised exercise. The other 2000 continue their usual habits. The researcher follows both groups for 5 years,
Select the correct explanation clearly detailing why the second design will produce more trustworthy data.
1) The first design is an observational study whereas the second design is an experiment. Assigning subjects to treatments, as in the second design, avoids confounding.
2) In the second design, the subjects are chosen in a random fashion, whereas in the first design the subjects from the second group are matched to the subjects in the first group.
3) The first design is an experiment whereas the second design is an observational study. Assigning subjects to treatments, as in the first design, does not avoid confounding.
4) In the first design, subjects are assigned to groups based on their own habits. There may be other factor (e.g., personality type or genetic background) that make one more likely to exercise and less (or more) likely to have a heart attack.