To measure physical activity, respondents were asked how often they engaged in physical activities of moderate intensity (i.e., brisk walking, bicycling, vacuuming, gardening, or anything else that causes small increases in breathing or heart rate) and vigorous intensity (i.e., running, aerobics, heavy yard work, or anything else that causes large increases in breathing or heart rate) for at least 10 minutes at a time in a usual week. Respondents were classified as being regularly active if they reported engaging in moderate-intensity activity at least 30 minutes per day, 5 or more days per week, or vigorous-intensity activity at least 20 minutes per day, 3 or more days per week. Respondents were classified as insufficiently active if they reported engaging in physical activity for at least 10 minutes per week, but did not meet the requirements for regular activity. Respondents who reported no instances of physical activity of ≥10 minutes' duration during a usual week were classified as inactive.