Does regular exercise reduce bone loss in postmenopausal women? Here are two ways to study this question. Which design will produce more trustworthy data? 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 five years.
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 supervised exercise. The other 1000 continue their usual habits. The researcher follows both groups for five years.
Select all statements that are true.

A placebo would be impractical in both 1 and 2.

1 is an observational study and 2 is an experiment.

1 and 2 are both observational studies.

The effect of a lurking variable, such as a condition that might affect someone's desire to exercise and their bone loss, is likely to be larger in 1 and less in 2 due to randomization.

1 and 2 are both experiments.

The effect of a lurking variable, such as a condition that might affect someone's desire to exercise and their bone loss, is likely to be larger in 2 and less in 1 due to randomization.