The Obesity Epidemic and Changes in Self-Report Biases in BMI

OBJECTIVE: To assess time trends in measurement error of BMI and the sensitivity/specificity of classifying weight status in the United States by analyzing the difference in BMI between self-reported and measured height and weight. DESIGN AND METHODS: Data from 18,394 respondents aged 20-89 years from the National Health and Nutrition Examination Survey (NHANES) from 1999 through 2008 were analyzed. Multiple linear regression and logistic regression models estimated trends in reporting bias and misclassification of weight status by BMI categories, sex, age, and racial/ethnic groups, adjusting for the sampling design. RESULTS: We find no evidence that there are time trends in the accuracy of self-report by BMI categories, sex, age, or racial/ethnic groups. The well-known downward bias in self-report has remained stable over the last decade; approximately one in six to seven obese individuals were misclassified as nonobese due to underestimation of BMI. CONCLUSION: Increases in obesity rates based on self-reported height and weight are likely to reflect actual weight increases and are not inflated by changes in reporting accuracy.