Expected years of life free of chronic condition-induced activity limitations - United States, 1999-2008.

Over the 20th century, the U.S. population has witnessed major changes in fatal and nonfatal health outcomes. Mortality has declined, and life expectancy has increased continuously; chronic conditions have replaced acute diseases as leading causes of both illness and death. During 1900-2008, average life expectancy at birth for the total U.S. population increased from 47.3 years in 1900 to 78.1 years in 2008, a gain of 30.8 years. In addition, an increasing proportion of the U.S. population is aged >65 years. According to the U.S. Census Bureau estimates, at the beginning of the 20th century, the U.S. population aged >65 years constituted only 4.1 percent of the total population; by 2008, the percentage of the total U.S. population aged >65 years was 12.8%. However, declines in mortality are not necessarily associated with declines in morbidity or the consequences of chronic conditions on life activities. The possibility that longer life might be accompanied by poor health makes it essential to develop measures that account for both mortality and morbidity at the same time. Hence, over the past 40 years, a new set of health measures (e.g., "healthy life expectancies") have been developed that account for both mortality and life spent free of the consequences of ill health. One of these newly developed set of measures (called "active life expectancy") is the average number of years expected to be lived without activity limitations.