Exercise and bone loss. Does regular exercise reduce bone loss in postmenopausal women? Here are two ways to study this question. Explain clearly why the second design will produce more trustworthy data.

1. A researcher finds 1000 postmenopausal women who exercise regularly. She matches each with a similar postmenopausal woman who does not exercise regularly, and she follows both groups for 5 years.

2. Another researcher finds 2000 postmenopausal women who are willing to participate in a study. She assigns 1000 of the women to a regular program of Chapter 5 Exercises 99 supervised exercise. The other 1000 continue their usual habits. The researcher follows both groups for 5 years.

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