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J R Soc Med. 2006 September; 99(9): 434–435.
PMCID: PMC1557888

Trends in obesity

Authors' reply

Gori raises two generic methodological issues that are empirically irrelevant in the specific analysis in our paper:

  1. The differences in response rate: BRFSS is the only available platform for monitoring obesity at the state level. Therefore, the relevant public health question is how to make its estimates comparable to NHANES, regardless of whether differences between BRFSS and NHANES are caused by individual reporting behaviour or lower response rate. The comparison of the two surveys is the correct way to address both sources of difference, as emphasized on page 250 of the paper.1
    Furthermore, analysis of NHANES and BRFSS at the national level shows that the difference between estimates from the two surveys is zero or small when respondents are not likely to misreport intentionally2. This result indicates that the underestimation of weight and height in BRFSS is more likely to be due to individual reporting behaviour than selection.
  2. Exclusion criterion: the exclusion criterion was applied only to NHANES (and not to ‘both surveys’), to exclude those subjects with missing data for either self-reported or measured height and weight in this survey. Table 1 shows that the NHANES height and weight figures are completely robust to this exclusion criterion.
    Table 1
    Age-standardized self-reported and measured height and weight in the National Health and Nutrition Examination Survey (NHANES) with and without exclusion of subjects who were missing either self-reported or measured data


Competing interests None declared.


1. Ezzati M, Martin H, Skjold S, Hoorn SV, Murray CJL. 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: 250-7 [PMC free article] [PubMed]
2. Nelson DE, Powell-Griner E, Town M, Kovar MG. A comparison of national estimates from the National Health Interview Survey and the Behavioral Risk Factor Surveillance System. Am J Public Health 2003;93: 1335-41 [PubMed]

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