title: Prediction equations do not eliminate systematic error in self-reported body mass index.
abstract: Epidemiological studies of the risks of obesity often use body mass index (BMI) calculated from self-reported height and weight. The purpose of this study was to examine the pattern of reporting error associated with self-reported values of BMI and to evaluate the extent to which linear regression models predict measured BMI from self-reported data and whether these models could compensate for this reporting error. We examined measured and self-reported weight and height on 5079 adults aged 30 years to 64 years from the second National Health and Nutrition Examination Survey. Measured and self-reported BMI (kg/m2) was calculated, and multiple linear regression techniques were used to predict measured BMI from self-reported BMI. The error in self-reported BMI (self-reported BMI minus measured BMI) was not constant but varied systematically with BMI. The correlation between measured BMI and the error in self-reported BMI was -0.37 for men and -0.38 for women. The pattern of reporting error was only weakly associated with self-reported BMI, with the correlation being 0.05 for men and -0.001 for women. Error in predicted BMI (predicted BMI minus measured BMI) also varied systematically with measured BMI, but less consistently with self-reported BMI. More complex models only slightly improved the ability to predict measured BMI compared with self-reported BMI alone. None of the equations were able to eliminate the systematic reporting error in determining measured BMI values from self-reported data. The characteristic pattern of error associated with self-reported BMI is difficult or impossible to correct by the use of linear regression models.
authors.affiliation: National Center for Health Statistics, Centers for Disease Control and Prevention, Hyattsville, MD 20782, USA.
authors.forename: M W
authors.initials: MW
authors.lastname: Plankey
authors.forename: J
authors.initials: J
authors.lastname: Stevens
authors.forename: K M
authors.initials: KM
authors.lastname: Flegal
authors.forename: P F
authors.initials: PF
authors.lastname: Rust
mesh_terms: D000328:Adult; D001827:Body Height; D015992:Body Mass Index; D001835:Body Weight; D005260:Female; D006306:Health Surveys; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D016353:Self-Examination; D012680:Sensitivity and Specificity