Accuracy of Body Mass Index Categories Based on Self-Reported Height and Weight Among Women in the United States

Abstract

Objective-The purpose of this study was to assess the accuracy of BMI categories based on selfreported height and weight in adult women. Methods-BMIcategories from self-reported responses were compared to categories measured during physical examination from women, age 18 or older, who participated in the National Health and Examination Survey, 1999Survey, -2004. We first examined strength of agreement using Cohen's kappa, which, unlike sensitivity and specificity, allows for the comparison of polychotomous measures beyond chance agreement. Kappa regression identifies potential threats to accuracy. Likelihood of bias, as measured by under-reporting, was examined using logistic regression.Results-Cohen's kappa estimates were 0.443 for pregnant women (N = 724) and 0.705 for nonpregnant women (N = 5,910). Kappa varied by age and race, but was largely unrelated to socioeconomic status, health and health behaviors. Women who visited a physician in the last year or been diagnosed with osteoporosis were more accurate, while women most likely to under-report were older, white, non-Hispanic, and college-educated.Conclusions-Our results suggest substantial agreement between self-reported and measured categories, except for women who are pregnant, above the age of 75 or without physician visits. Under-reporting may be more prevalent in well-educated, white populations than minority populations. KeywordsObesity; Body mass index; Cohen's kappa Obesity is a major public health epidemic and is an important risk factor contributing to morbidity and mortality from diseases such as heart disease, diabetes and cancer [1]. One of the challenges facing epidemiologists studying trends in the obesity epidemic is tracking changes over time. Both epidemiologists and clinicians often rely on self-reported height and weight, which are then used to calculate body mass index (BMI). Many studies have examined the accuracy of self-reported height, weight and BMI in a variety of cohorts [2][3][4][5][6] Fewer studies have examined the accuracy of self-reported height and weight when they are used to determine BMI categories [7][8][9][10]; yet, BMI categories are routinely used in studies of health outcomes [3]. Many of these studies showed significant differences in allocation to BMI categories based on self-reported versus measured height and weight, thus biasing relative risks of diseases associated with increasing BMI [3][4][5][6][7][8].In women, bias in self-reported height and weight may occur due to social desirability, cultural or demographic characteristics or health characteristics (such as pregnancy or osteoporosis) [9]. In general, women tend to under-report weight more than men [2], while men tend to overreport height more than women [6]. It is important to examine the potential threats to accuracy particular to women since under-or over-reporting may affect the prevalence and categorization of BMI differently among women than among men. Understanding of sources of bias among women is important in planning and interpreting e...

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