The Impact of Differences in Methodology and Population Characteristics on the Prevalence of Hypertension in US Adults in 1976-1980 and 1999-2002

BACKGROUND Results from the National Health and Nutrition Examination Survey (NHANES) indicate that hypertension prevalence declined by 9% points from 34% in 1976-1980 to 25% in 1999-2002 in adults 20-74 years. The purpose of this study was to estimate the impact on hypertension prevalence of measurement error and selected risk factors. METHODS Using cross-sectional survey data from NHANES, we estimated the effect on hypertension of incorrect blood pressure (BP) cuff size and zero end-digit preference and the effect of changes in the distribution of age, body mass index (BMI), sex, race-ethnicity, smoking, and education. The analytic sample of persons 20-74 years consisted of 11,563 from 1976-1980 and 7,901 from 1999-2002 NHANES. Covariate-adjusted prevalences were calculated using log-linear regression models to produce predictive margins. RESULTS After adjustment to age, BMI, sex, race-ethnicity, smoking, and education, the prevalence difference became higher, changing from -9% (95% confidence interval (Cl): -11, -6) to -14% (95 Cl: -17, -11). After adjustment to these risk factors and correction for measurement error the prevalence difference was -9% (95 Cl: -11, -6). CONCLUSIONS Measurement error, mainly from cuff size differences, inflated the temporal decline in hypertension prevalence. The results indicate that age, sex, race-ethnicity, smoking, or education did not fully explain the lower prevalence of measured hypertension in all BMI groups and suggest that a change in some unmeasured factor or factors contributed to the decline.