to such a focus is an important role for economic, behavioral, and social factors, whether manifested at the individual or population level. For it is to these factors that we will largely have to look to develop a complete explanation of core epidemiologic observations concerning group and geographic differentials in the prevalence and incidence of disease and time trends in disease. In what follows we will review selected information on variations in life expectancy and the occurrence of a number of major public health problems and discuss how such a multilevel approach provides critical perspectives on the causes of these variations and on opportunities to reduce them.
Overall life expectancy at birth reached 76.5 years in the United States in 1997, with almost steady increases since 1950 (NCHS, 1999). Since 1980, life expectancy at birth increased by 5.1% for males to 73.6 years, and by 2.6% for females to 79.4 years, and life expectancy at age 65 increased by 12.8% to 80.9 years, and by 4.9% to 84.2 years, for males and females, respectively. Despite these increases the United States still compares poorly to many countries—ranking twenty-fifth for males and nineteenth for females on a list of 36 countries compiled by the National Center for Health Statistics (NCHS, 1999).