The first National Health and Nutrition Examination Survey (NHANES I) was conducted by the National Center for Health Statistics between 1971 and 1974. NHANES I was a clustered, multi-stage stratified probability sample of 23,808 individuals ranging in age from one to 74 years and drawn from the non-institutionalized civilian population of the United States. A random subsample of the 14,407 examined adults aged 25-74 were given supplemental questionnaires on cardiovascular and respiratory history.