Accuracy and usefulness of BMI measures based on self-reported weight and height: findings from the NHANES &amp; NHIS 2001-2006

Manfred Stommel,Charlotte A Schoenborn

doi:10.1186/1471-2458-9-421

Abstract

BackgroundThe Body Mass Index (BMI) based on self-reported height and weight ("self-reported BMI") in epidemiologic studies is subject to measurement error. However, because of the ease and efficiency in gathering height and weight information through interviews, it remains important to assess the extent of error present in self-reported BMI measures and to explore possible adjustment factors as well as valid uses of such self-reported measures.MethodsUsing the combined 2001-2006 data from the continuous National Health and Nutrition Examination Survey, discrepancies between BMI measures based on self-reported and physical height and weight measures are estimated and socio-demographic predictors of such discrepancies are identified. Employing adjustments derived from the socio-demographic predictors, the self-reported measures of height and weight in the 2001-2006 National Health Interview Survey are used for population estimates of overweight & obesity as well as the prediction of health risks associated with large BMI values. The analysis relies on two-way frequency tables as well as linear and logistic regression models. All point and variance estimates take into account the complex survey design of the studies involved.ResultsSelf-reported BMI values tend to overestimate measured BMI values at the low end of the BMI scale (< 22) and underestimate BMI values at the high end, particularly at values > 28. The discrepancies also vary systematically with age (younger and older respondents underestimate their BMI more than respondents aged 42-55), gender and the ethnic/racial background of the respondents. BMI scores, adjusted for socio-demographic characteristics of the respondents, tend to narrow, but do not eliminate misclassification of obese people as merely overweight, but health risk estimates associated with variations in BMI values are virtually the same, whether based on self-report or measured BMI values.ConclusionBMI values based on self-reported height and weight, if corrected for biases associated with socio-demographic characteristics of the survey respondents, can be used to estimate health risks associated with variations in BMI, particularly when using parametric prediction models.

Highlights

The Body Mass Index (BMI) based on self-reported height and weight ("selfreported BMI") in epidemiologic studies is subject to measurement error
It remains important to assess the extent of error present in BMI measures that are based on self-reported height and weight compared with BMI measures based on physical measurement of height and weight and to understand the limitations of using the self-reported measures
In a study of Mexican citizens, others found that BMI values calculated from self-reported height and weight underestimated BMI values based on measured height and weight --- a tendency that increased with age [7]

Summary

Introduction

The Body Mass Index (BMI) based on self-reported height and weight ("selfreported BMI") in epidemiologic studies is subject to measurement error. The use of the Body Mass Index (BMI) based on selfreported height and weight in epidemiologic studies remains controversial, both because it is an imperfect measure of a person's percentage of body fat [1] and because self-reported height and weight are subject to substantial measurement error [2]. In a study of Mexican citizens, others found that BMI values calculated from self-reported height and weight underestimated BMI values based on measured height and weight --- a tendency that increased with age [7]. A similar pattern seems to hold for non-Hispanic African American adults, for whom BMI values computed from self-reported height and weight seem to produce smaller underestimates of their measured BMIs than among non-Hispanic whites [6,8]. There is strong evidence that the actual BMI itself is a predictor of the error in BMI measures based on selfreported height and weight, with underestimates of BMI becoming larger for respondents with higher-end weight and BMI values [11,12,13]

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