Objective: The purpose of this study was to assess the accuracy of BMI categories based on self-reported height and weight in adult women.
Methods: BMI categories 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, 1999-2004. 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 non-pregnant 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.