Trends in national and state-level obesity in the USA after correction for self-report bias: analysis of health surveys

Abstract

Objectives: To quantify population-level bias in self-reported weight and height as a function of age, sex, and the mode of self-report, and to estimate unbiased trends in national and state level obesity in the USA.

Design: Statistical analysis of repeated cross-sectional health examination surveys (the National Health and Nutrition Examination Survey [NHANES]) and health surveys (the Behavioral Risk Factor Surveillance System [BRFSS]) in the USA.

Setting: The 50 states of the USA and the District of Columbia.

Results: In the USA, on average, women underreported their weight, but men did not. Young and middle-aged (<65 years) adult men over-reported their height more than women of the same age. In older age groups, over-reporting of height was similar in men and women. Population-level bias in self-reported weight was larger in telephone interviews (BRFSS) than in-person interviews (NHANES). Except in older adults, height was over-reported more often in telephone interviews than in-person interviews. Using corrected weight and height in the year 2000, Mississippi (30%) and Texas (31%) [corrected] had the highest prevalence of obesity for men; Texas (37%), Louisiana (37%), Mississippi (37%), District of Columbia (37%), Alabama (37%), and South Carolina (36%) for women.

Conclusions: Population-level bias in self-reported weight and height is larger in telephone interviews than in-person interviews. Telephone interviews are a low-cost method for regular, nationally- and sub-nationally representative monitoring of obesity. It is possible to obtain corrected estimates of trends and geographical distributions of obesity from telephone interviews by using systematic analysis which measure weight and height from an independent sample of the same population.

Figure 1

Measured (National Health and Nutrition Examination Survey [NAHNES]) and self-reported (NHANES in-person and Behavioral Risk Factor Surveillance System [BRFSS] telephone) BMI by age and sex. Each data point shows the 95% confidence interval (CI) for estimated body mass index as two horizontal lines. When the 95% CI is small, the two horizontal lines appear to overlap. This is particularly the case for BRFSS (shown in red), which has very large sample size. For each survey, a local (non-parametric) regression was used to estimate the age pattern, shown as solid lines.

Figure 2

Measured (National Health and Nutrition Examination Survey [NAHNES]) and self-reported (NHANES in-person and Behavioral Risk Factor Surveillance System [BRFSS] telephone) height and weight by age and sex. Each data point shows the 95% confidence (CI) for estimated body mass index as two horizontal lines. When the 95% CI is small, the two horizontal lines appear to overlap. This is particularly the case for BRFSS (shown in red), which has very large sample size. For each survey, a local (non-parametric) regression was used to estimate the age pattern, shown as solid lines.

Figure 3

Self-reported height and weight in Behavioral Risk Factor Surveillance System (BRFSS) telephone surveys in relation to measured height and weight from National Health and Nutrition Examination Survey (NAHNES). Each point represents one 5-year age group (i.e. see the points in Figure 2), shown in blue for 1988-1994 and in red for 1999-2002

Figure 4

Trends in mean body mass index and obesity in men and women in the USA, based on self-reported Behavioral Risk Factor Surveillance System (BRFSS) height and weight as well as corrected height and weight. All values are age-standardized to the 2000 USA population

Figure 5

Prevalence of obesity in USA states in (a) 1990 and (b) 2000, based on self-reported Behavioral Risk Factor Surveillance System (BRFSS) height and weight as well as corrected height and weight. All values are age-standardized to the 2000 USA population.