The declining contribution of socioeconomic disparities to the racial gap in infant mortality rates, 1920-1970.

• Author: Collins, William J.

1. Introduction

   Great improvements in physical health are among the 20th century's most impressive social achievements. In the United States, life expectancy at birth increased by more than 25 years (Atack and Passell 1994), average height increased by about 7 centimeters for native-born white males (Costa and Steckel 1997), and a number of deadly diseases and debilitating illnesses were all but vanquished. As the population's overall level of health improved, racial gaps in health outcomes persisted. Such gaps remain a serious concern for U.S. policymakers (Department of Health and Human Services 2000; Levine et al. 2001; Byrd and Clayton 2002). In large part, this is because physical health is a direct determinant of well being. Additionally, because one's health may influence educational attainment, labor force participation and productivity, and one's children's health, the consequences of intergroup health disparities may be quite far reaching (Grossman 1975; Edwards and Grossman 1979; Currie and Hyson 1999).

   In discussions of intergroup health differences, infant mortality is a frequently referenced barometer. As shown in Figures 1 and 2, the overall infant mortality rate (deaths under 1 year of age per 1000 live births) and the absolute (nonwhite-white) racial gap in infant mortality rates fell over time, but nonwhite infants were always more likely to die than white infants. In fact, on average, nonwhite infants were about 75% more likely to die than white infants during the 20th century. When translated Into numbers of "excess" deaths, it is clear that the racial gap remained nontrivial even as it narrowed in absolute terms: In 1940, approximately 8900 more nonwhite infants died than would have if they had had the same mortality rate as whites; in 1970, the excess was approximately 8400 infants. (1)

   The literature on infant mortality is voluminous and multifaceted, but relatively few studies have systematically examined how racial gaps in infant mortality changed in the early and mid-20th century, choosing instead to focus on more recent data (see inter alia, Rochester 1923; Woodbury 1925; Shapiro, Schlesinger, and Nesbitt 1968; Chase 1972; Shin 1975; Grossman and Jacobowitz 1981; Ewbank 1987; David and Collins 1997; Department of Health and Human Services 2000). Understanding the racial gap and its movement in the earlier period is important for at least three reasons. First, by far the largest improvements in infant mortality, and the largest declines in the black-white gap, occurred before 1970. Historical experience therefore provides perspective on the magnitude of contemporary infant mortality levels, changes, and disparities. Second, the most striking, and puzzling, aspect of the post-1970 experience is that racial disparities in socioeconomic characteristics account for less than half of the racial gap in infant mortality rates (Hecht and Cutright 1979; Miller 2001; Cutler and Meara 2003). We find that this was not always the case; rather, the large "unexplained" portion of the gap emerged gradually in the postwar period. Consequently, researchers and policymakers interested in understanding the origins of the large unexplained residual may benefit from closer empirical scrutiny of the pre-1970 period. Third, for most of the 20th century, prevailing patterns of racial discrimination embedded themselves in the health care system, perhaps compounding the disadvantages that African Americans already faced due to their geographic distribution and relative lack of financial and educational resources. The health implications of racial segregation (and desegregation) have not been adequately documented, especially for the period when segregation was most intense.

   In this paper, we explore state-level infant mortality data in a framework that sheds light on both the declining overall level of infant mortality and the racial gap. After discussing the interaction of race, history, and infant mortality in the context of a simple model of demand for and supply of health care, we construct and analyze a panel of state-level data for whites and nonwhites. Our analysis focuses on the 1920 to 1970 period because, as noted already, it is underexplored despite experiencing levels and changes in mortality that dwarf those of the last 30 years. We make efforts to link our findings to the existing literature on the post-1970 period, but we do not attempt to reexamine data for the later period. In part, this is because major shifts in social policy, especially the legalization of abortion, add a layer of complexity that cannot be adequately treated in the space of this paper. Additionally, large infant-level datasets are available to researchers for analysis of the later period, and it is unlikely that extending a state-level analysis to later years could yield more insight than the micro-level studies already have.

   We find that differences in income, women's education, urban residence, and the supply of physicians can account for a large portion of the racial gap in infant mortality rates from 1920 to 1945, but that they account for a declining proportion of the gap thereafter. We also find that although there was a strong secular decline in infant mortality for both races, the racial gap did not narrow continuously over time. We discuss the post-1940 period in light of changes in birth weight, maternal characteristics, smoking and breast-feeding behavior, air pollution, and institutional changes that may have influenced access to professional medical care. Some of these trends tended to widen the racial infant mortality gap even as movements in fundamental socioeconomic characteristics tended to narrow it.

2. Conceptual Framework and Historical Context

   Our interpretation is guided by a simple model of infant mortality in which the likelihood of an infant's death is influenced the family's consumption of quality-adjusted units of nutrition, housing, health-related information, and health services. For convenience, we refer to this bundle of goods as health care (broadly speaking), and we think of it as an intermediate input in an infant health production function. (2) Infant health may also vary because of changes in the disease environment and because of variation in families' (especially mothers') initial endowments of human capital (a combination of health, knowledge, and responsiveness to health-related information). Of course, it may also be influenced by changes in technology, policy, and health-related institutions. This section begins by discussing the technology of infant medical care. Next, it identifies several factors that influenced racial disparities in health care (and therefore in health outcomes) throughout the 1920 to 1970 period. Finally, it highlights the major governmental interventions that targeted maternal and infant health.

   The Technology of Infant Medical Care

   Medical technology can reduce infant mortality in either the neonatal period (birth to 28 days) or the postneonatal period (28 days to 1 year). Neonatal infant mortality typically results from congenital defects, birth injury, and low birth weight (under 2500 grams), while postneonatal infant mortality is more likely to result from environmental factors such as communicable disease. Early in the 20th century, medical technology held few benefits for either neonates or postneonates. In 1900, only about 5% of all births occurred in hospitals (Wertz and Wertz 1989). At the time, the benefits of hospital and physician-attended birth were slim, and hospitals and physicians could do little to improve the health of unhealthy newborns. The better hospitals strove to be aseptic, but general practitioners were poorly trained and probably no better at delivering infants than midwives (Wertz and Wertz 1989).

   After 1900, the accumulation of clinical experience at hospitals, reforms in medical education following the Flexner Report in 1910, and the rise of specially trained obstetricians increased the advantages of hospital births, particularly for complicated deliveries. Increases in urbanization and insurance coverage, along with refinements in pain-relieving procedures, meant that birth became a predominantly hospital-based activity by midcentury. In 1955, 94% of deliveries took place in hospitals where doctors could assist mothers with anesthetics, drugs to speed up delivery, X-ray machines to detect pelvic abnormalities, fetal heart monitoring equipment, and cesarean sections (Wertz and Wertz 1989). These improvements helped reduce neonatal infant mortality from birth injuries from 4.8 to 2.4 deaths per 1000 births from 1930 to 1960 (Linder and Grove 1943; Grove and Hetzel 1968).

   The slow accumulation of clinical experience (e.g., in feeding) and technological advances (e.g., in incubators and drug therapies) contributed to a steady decline in neonatal infant mortality due to noninjury reasons (predominantly, low birth weight) up to 1950 (Costa 1998). But great strides in caring for unhealthy neonates, particularly those with low birth weights, were made relatively recently. While special nurseries equipped with incubators existed in many cities in the 1940s (Corwin 1952; Cone 1985), the mortality rate for low birth weight infants remained high: In both 1950 and 1960, about 170 per 1000 low birth weight infants died as neonates (Chase 1972). It was not until the introduction of modern neonatal intensive care units (NICUs) in the late 1960s--and significant refinements in ventilation techniques--that the mortality rate of low birth weight infants declined significantly. By 1983, the mortality rate of low birth weight infants had fallen to 96 deaths per 1000 births (National Center for Health Statistics 2001).

   Improved medical technologies contributed to dramatic reductions in posmeonatal infant mortality before midcentury. In particular, two leading causes of postneonatal infant death, pneumonia and gastroenteritis, could be...