Misreporting and Misclassification: Implications for Socioeconomic Disparities in Body-mass Index and Obesity

Body-mass index (BMI), sometimes calculated from objectively measured and sometimes from self-reported weight and height, has become the standard proxy for obesity in social science research. This study deals with the potential problems related to, first, relying on self-reported weight and height to calculate BMI (misreporting), and, second, the concern that BMI is a deficient measure of body fat and elevated health risks (misclassification). Using a regional Swedish sample, we analyze whether socioeconomic disparities in BMI are biased because of misreporting, and whether socioeconomic disparities in the risk of obesity are sensitive to whether BMI or waist circumference is used to define obesity. Education and two income measures are used as socioeconomic indicators. Among women, different educational groups misreport differently, leading to underestimation of the education disparity when using self-reported information. Among men, misreporting is un-related to socioeconomic status, but misclassification is related to education. As a consequence, when estimating the risk of obesity defined using waist circumference, an educational gradient, which is not present when classifying men using BMI, arises. Taken together, female disparities appear more sensitive to whether weight and height are self-reported, whereas male disparities are more sensitive to definition of obesity.