1.45 We all know that exercise is good for us. But can exercise prevent or delay the symptoms of Parkinson’s disease? A recent study by the Harvard School of Public Health studied 48,000 men and 77,000 women who were relatively healthy and middle-aged or older. During the course of the study, the disease developed in 387 people. The study found that men who had participated in some vigorous activity at least twice a week in high school, college, and up to age 40 had a 60% reduced risk of Parkinson’s disease developing. The study found no such reduction for women. What type of sampling does this represent?

Source: Exercise may prevent Parkinson’s, USA Today, February 22, 2005, p. 7D