The National Center for Health Statistics (NCHS) conducts an extensive survey consisting of an interview and medical examination with a representative sample of about 5000 people a year. The interview includes demographic, socioeconomic, dietary, and other health-related questions. The examination “consists of medical, dental, and physiological measurements, as well as laboratory tests administered by highly trained medical personnel” (www.cdc.gov/nchs/nhanes/ about_nhanes.htm). Describe the sample, the population, the Who and the What of this study.