Trends in health in the United States.

The National Center for Health Statistics (NCHS) conducts a variety of surveys designed to provide cross-sectional estimates of the prevalence of various factors measuring the health of Americans. When these cross-sectional estimates are put together and plotted over time, they provide a picture of the trends in the health of the population. However, differences in methodology, completeness of coverage, validity and reliability of the information, and changing attitudes about health and illness influence these trend patterns and sometimes make them difficult to interpret. Six different measures of the health of Americans discussed include trends in life expectancy, which is related to the total mortality rate; trends in mortality by specific causes; trends in morbidity or the prevalence of various illnesses, including both acute and chronic conditions; trends in the estimates of various types of disabilities and impairments in the population; trends in expenditures for medical care and services; and finally, some assessments of trends in several risk factors and physiological characteristics obtained by direct measurements of individuals.