2.4. Covariates
Subject age and gender were used as reported in the public-use NHANES
data. We used the racial and ethnic group variable reported by NHANES
based on survey responses to questions about racial group and ethnicity.
We combined responses from the NHANES categories of Mexican-
American and Other Hispanic into a single Hispanic category according
to analytic guidelines [7]. Otherwise, we used the racial/ethnic groups
as reported by NHANES. We included household income as a measure
of socioeconomic status, categorized as $0–19 999, $20 000–34 999,
$35 000–74 999, and $75 000. A personal history of diabetes or gout
was identified from the medical examination component, as was BMI,
which was categorized as normal weight (18.0–24.9 kg/m2), overweight
(25.0–29.9 kg/m2), and obese (30.0 kg/m2).