Body mass index (BMI) was computed from self-reported weight in kilograms divided by self reported height in meters squared and was available for 41 654 respondents. Although self-reports of height and weight tend to underestimate BMI somewhat (Roberts, 1995), they are highly correlated with direct physical measurement (Cash, Counts, Hangen, & Huffine, 1989). Respondents were classified into three groups based on established guidelines (National Heart, Lung, and Blood Institute, 1998). Those with BMI values of 18.5 to 24.9 were in the normal weight category, respondents with a BMI of 25 to 29.9 were classified as overweight, and respondents with a BMI of 30 or greater were classified as obese. Individuals classified as underweight (BMI < 18.5) were excluded from the current analyses because the number of underweight individuals, particularly underweight men, was very small compared to the other BMI categories. Excluding underweight individuals left data for 40 790 respondents. Because pregnancy can temporarily increase BMI, pregnant women were also excluded, leaving a sample of 40 364.
