The infant mortality rate (which is commonly calculated as the number of deaths among infants under 1 year of age in a calendar year per 1,000 live births in that year) measures the probability that a newborn baby will survive the hazards of infancy and live to celebrate his or her first birthday. Whether a given infant survives this crucial first year of life is influenced in part by certain biological characteristics (e.g., genetic makeup, nature of the birth outcome, susceptibility to particular diseases). But a voluminous body of research over the past century has clearly identified the major determinants of the overall infant mortality rate to be, first, the nature of the physical environment, especially the state of sanitation, and, second, the nature and availability of health care facilities. Although the health of persons of all ages is affected by these conditions, the newborn infant is most susceptible and most likely to be adversely affected by the absence of appropriate sanitary and health care facilities.

It has also been solidly established that within any society infant mortality rates are strongly related to family income, which in turn is an indicator of both the nature of the environment in which an infant is born and raised and the family’s ability to provide the infant with optimal health care. The basic aim of this essay is to review briefly some of the relevant research and to present empirical justification for designating the infant mortality rate as the most sensitive indicator of the overall health status of any population group.