Prediction of Body Mass Index Using Concurrently Self-Reported or Previously Measured Height and Weight

Objective To compare alternative models for the imputation of BMI M (measured weight in kilograms/measured height in meters squared) in a longitudinal study. Methods We used data from 11,008 adults examined at wave III (2001–2002) and wave IV (2007–2008) in the National Longitudinal Study of Adolescent to Adult Health. Participants were asked their height and weight before being measured. Equations to predict wave IV BMI M were developed in an 80% random subsample and evaluated in the remaining participants. The validity of models that included BMI constructed from previously measured height and weight (BMI PM ) was compared to the validity of models that used BMI calculated from concurrently self-reported height and weight (BMI SR ). The usefulness of including demographics and perceived weight category in those models was also examined. Results The model that used BMI SR , compared to BMI PM , as the only variable produced a larger R 2 (0.913 vs. 0.693), a smaller root mean square error (2.07 vs. 3.90 kg/m 2 ) and a lower bias between normal-weight participants and those with obesity (0.98 vs. 4.24 kg/m 2 ). The performance of the model containing BMI SR alone was not substantially improved by the addition of demographics, perceived weight category or BMI PM . Conclusions Our work is the first to show that concurrent self-reports of height and weight may be more useful than previously measured height and weight for imputation of missing BMI M when the time interval between measures is relatively long. Other time frames and alternatives to in-person collection of self-reported data need to be examined.