Oatmeal and cholesterol. Does eating oatmeal reduce the level of bad cholesterol (LDL)? Here are two ways to study this question.

1. A researcher finds 500 adults over 40 who regularly eat oatmeal or products made from oatmeal. She matches each with a similar adult who does not regularly eat oatmeal or products made from oatmeal. She measures the bad cholesterol (LDL) for each adult and compares both groups.
2. Another researcher finds 1000 adults over 40 who do not regularly eat oatmeal or products made from oatmeal and are willing to participate in a study.
She randomly assigns 500 of these to a diet that includes a daily breakfast of oatmeal. The other 500 continue their usual habits. After 6 months, she compares changes in LDL levels.

(a) Explain why the first is an observational study and the second is an experiment.

(b) Why does the experiment give more useful information about whether oatmeal reduces LDL?AppendixLO1