Health is a state of complete physical, mental, and social well-being, and not the mere absence of disease or infirmity.¹ An overarching goal of public health agencies is to increase the quality and years of healthy life and to eliminate health disparities. Tracking historical trends in general health status can help identify where interventions have improved the health of a population or where interventions may be needed (e.g., by exploring causative factors and preventive measures).

For example, at the beginning of the 20^th century, the U.S. population was characterized by a low standard of living, poor hygiene, and poor nutrition; communicable diseases and acute conditions were major causes of most premature deaths. Over the course of the century, public health measures such as improved sanitation and drinking water treatment led to a dramatic decrease in deaths due to infectious diseases and a marked increase in life expectancy.

As the population has aged, chronic diseases such as heart disease and cancer have become the leading causes of death. These diseases may require a different approach to prevention, detection, and treatment compared to the infectious and acute illnesses more common in the past. ^2,3

The health status of a population can be measured by a wide range of factors: birth and death rates, life expectancy, quality of life, morbidity from specific diseases, risk factors, use of ambulatory care and inpatient care, accessibility of health personnel and facilities, financing of health care, health insurance coverage, and many other factors.⁴

While no single set of measures can completely characterize the health of a large and diverse population, the Centers for Disease Control and Prevention (CDC) and other health agencies worldwide consistently have viewed life expectancy and mortality data as indicators of overall population health because they represent the cumulative effects of social and physical environmental factors, behavioral and genetic risk factors, and the level and quality of health care.

These data include the leading causes of mortality (among both infants and the general population), and thus provide a broad perspective on the diseases and conditions that are having the greatest impact on the nation's health. Infant mortality is a particularly useful measure of health status, because it:

• Indicates the current health status of a population.
• Predicts the health of the next generation.⁵
• Reflects the overall state of maternal health, as well as the quality and accessibility of primary health care available to pregnant women and infants.

The ROE presents three widely accepted measures to assess trends in health status in the United States: General Mortality, Infant Mortality, and Life Expectancy.

• General mortality represents the number of all deaths nationwide and provides information on the leading causes of death. Mortality is also tracked using years of potential life lost, or the number of years “lost” by people in a population who die prematurely of a stated cause.
• Infant mortality is the number of infants who die before their first birthday.
• Life expectancy is the average number of years a newborn would be expected to live if current death rates were to remain constant.

These indicators (which all rely on data from CDC's National Center for Health Statistics) are interrelated. For example:

• Declines in mortality result in increased life expectancy.
• Shifts in life expectancy are often used to describe changes in mortality.
• Changes in infant mortality are reflected in general mortality as well.

Overall, the ROE Health Status indicators show improved health status in the U.S. population over time, although racial and ethnic disparities persist. In addition, life expectancy is lower and infant mortality rates are higher in the United States compared with many other developed countries.

The three ROE health status indicators can be compared with data from the World Health Organization (WHO), which calculates health statistics for its 194 "member states". (Note that the WHO uses an approach that ensures comparability across data sets; its statistics may not fully match those generated by individual countries and reported in other reports.)

• Life expectancy: In 2016, 33 of the 194 WHO member states reported longer life expectancies at birth than in the United States for both males and females combined.⁶ Japan reports the highest life expectancy at 84.2 years ⁷, compared to the U.S. life expectancy of 78.8 years (Life Expectancy indicator).
• Leading causes of death: The top five leading causes of death reported in the United States in 2015 were heart disease, cancer (malignant neoplasms), chronic lower respiratory diseases, accidents (unintentional injuries), and stroke (cerebrovascular) (General Mortality indicator).
  
  The most recent worldwide data (2016) show that cardiovascular diseases (i.e., ischemic coronary heart disease and stroke) accounted for the largest percentage of deaths (27 percent). Chronic obstructive pulmonary disease (5.4 percent) and lower respiratory infections (5.2 percent) are, respectively, the third and fourth causes of death reported worldwide. Alzheimer’s disease and other dementias (3.5 percent) now rank as the fifth leading cause of death worldwide. Cancer of the trachea, bronchus, and lung (3.0 percent), diabetes mellitus (2.8 percent), road injury (2.5 percent), diarrheal diseases (2.5 percent), and tuberculosis (2.3 percent) follow.⁸
• Infant mortality: In 2015, 44 of the 194 WHO member states reported lower infant mortality rates than the United States. For example, five WHO member states (Iceland, Slovenia, Finland, Japan, and Luxembourg) have infant mortality rates of two or fewer deaths per 1,000 live births ⁹, compared to the U.S. infant mortality rate of 5.9 infant deaths per 1,000 live births (Infant Mortality indicator).

The three health status indicators presented have some limitations.

• While environmental contaminants can influence public health, so can many other factors, including socio-demographic attributes, behavioral and genetic risk factors, level of preventive care, and quality of and access to health care. Therefore, the health status indicators presented here are broad, are not intended to represent specific diseases or conditions related to the environment, and cannot alone be used to draw conclusions about how exposure to environmental contaminants influences public health. They do, however, provide important context for indicators of trends in human disease and conditions for which environmental contaminants may be a risk factor.
• While declining death rates and increasing life expectancy suggest improving health status, these indicators do not address other aspects of health, such as morbidity, perceived well-being, or quality of life, for which data are not available on a national scale.
• Improved data (including standardized data collection) on the health status of population subgroups—particularly across race and ethnic groups—would allow better characterization of potential trends across different groups for the three indicators presented.