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06. Body Mass vs. Body Fat

Cawley and Burkhauser

(l.) John Cawley, (r.) Richard Burkhauser

John H. Cawley and Richard V. Burkhauser, Policy Analysis and Management, analyzed measures of obesity and developed a tool for better accuracy. Although medical literature has long shown that percent of body fat is a more accurate measure of fatness than body mass index (BMI), social science researchers still rely on BMI, because it is used in most social science–based data sets. Cawley and Burkhauser have created a conversion tool that enables researchers to calculate percent of body fat and other more accurate measures of obesity for social science data sets that contain only information on height and weight. When researchers use percent-of-body-fat data to assess obesity rather BMI, for example, the huge gap in obesity rates between African-American and white women is halved, and white men have a much higher risk of obesity than African-American men. Because BMI ignores the difference between fat and fat-free mass, such as bone and muscle, it overstates the obesity of African Americans (with more nonfat mass) relative to whites. The researchers also found indications of a correlation between high percentages of body fat and employment disability, which could not have been determined using BMI.

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