3.96 Calcium and healthy bones. Adults need to eat foods or supplements that contain enough calcium to maintain healthy bones. Calcium intake is generally measured in milligrams per day (mg/d), and one measure of healthy bones is total body bone mineral density measured in grams per centimeter squared (TBBMD, g/cm²). Suppose that you want to study the relationship between calcium intake and TBBMD.

1. (a) Design an observational study to study the relationship.

2. (b) Design an experiment to study the relationship.

3. (c) Compare the relative merits of your two designs. Which do you prefer? Give reasons for your answer.