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Obesity rates in U.S. states may be underestimated
Self-reporting weight and height may present problems with bias.
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When asked their height and weight, volunteers in national health surveys tend to underreport their weight and overreport their height, which may have skewed national estimates of obesity, according to researchers at the Harvard School of Public Health.
Majid Ezzati, PhD, associate professor of international health at the Harvard School of Public Health, told Endocrine Today that an analysis he conducted with his colleagues presents the first unbiased picture of the nation’s obesity.
“This study shows us the first estimates of obesity in the 50 U.S. states and the District of Columbia that has corrected for how people report their own weight and height,” Ezzati said.
Ezzati’s analysis, published in a recent Journal of the Royal Society of Medicine, suggests that obesity is a Southern problem in the United States, and that in individual states it may have been previously underreported by more than 50%.
Cynthia Ogden, PhD, an epidemiologist at the Centers for Disease Control and Prevention, has had research recently published in the Journal of the American Medical Association regarding obesity rates in the U.S. (see Endocrine Today, May, page 40, “Obesity Unchanged in women from 1999 to 2004”).
She did not dispute that self-reporting creates a certain level of bias, but she said the national data self-reported estimates are two-thirds of the estimate based on measured data.
Policymaking
Ezzati said that as interest in the obesity epidemic in America turns to action, it is important to have the most accurate numbers possible.
“The CDC publishes their annual state-level figures with the caveat that they have a self-reporting bias, but if we are going to make policy we need to have a number that is as close as possible, not a number we know is wrong,” Ezzati said.
Ogden told Endocrine Today that she agreed with the criticism that self-reporting bias leads to questionable prevalence data, but the data remain useful for comparisons.
“Even with self-reporting we see that the prevalence has risen over time, and it provides us with a sample that we can use to compare states with other states,” Ogden said.
Ezzati and colleagues evaluated data from the Behavioral Risk Factor Surveillance System (BRFSS) and the National Health and Nutrition Examination Survey (NHANES). BRFSS uses telephone interview and NHANES uses in-person interview with subsequent measurement.
BMI underreported
When Ezzati and colleagues compared the results of self-report with in-person evaluation, they found that BMI was underreported for every demographic except for young men in-person interviews only.
The self-reporting bias was greater for women than for men, especially among the young and the middle-aged, according to the paper.
On average, American men did not underestimate their weight, but women did, especially during telephone interviews. Both men and women overestimated their height, though men did so by a larger amount.
The corrected 2002 rate of obesity among men was 28.7%, which was 6.8 percentage points higher than the rate seen with telephone self-reporting.
Among women, the 2002 corrected rate was 34.5%, which was 13.3 percentage points higher than the self-report.
Using corrected weight and height for the year 2000, Texas had the highest prevalence of obesity among men at 31%, followed by Mississippi at 30%. Among women, Texas, Louisiana, Mississippi, South Carolina, Washington D.C. and Alabama all had a 36% to 37% rate of obesity.
For more information:
- Ezzati M, Martin H, Skjold S, et al. Trends in national and state-level obesity in the USA after correction for self-report bias: analysis of health surveys. J R Soc Med. 2006;99:250-257.