Cause of Death

To understand more fully the association between income status and levels of infant mortality it is necessary to undertake a cause-specific analysis to see if the general inverse nature of the relationship can be explained largely in terms of a few selected causes or groups of causes, or if it more or less characterizes all the major causes of death. In this analysis, the census tracts were grouped into three rather than five income aggregates. A preliminary examination of the data indicated that a larger number of groupings would introduce a serious problem of rate instability because of smaller cell frequencies in the more detailed cross-tabulations. Even with only three areas, small frequencies became a problem when specific causes of death were considered; hence, this analysis was confined to the total population, and most of the comparisons were limited to two broad categories of causes of death. These are exogenous causes of death (those whose origin is farthest removed from the actual birth process) and endogenous causes of death (those whose origin is most closely associated with the physiological processes of gestation and birth). The specific cause groups, along with their identification codes from the ninth revised edition of the International Statistical Classification of Diseases and Causes of Death, are as follows:

Exogenous causes

Infectious and parasitic causes (001-139, 320—3,

460-6, 480-7, 500-8, 771) Injury or poisoning (800-999)

Endogenous causes

Congenital anomalies (740-59)

Conditions originating in the perinatal period (760-

Residual endogenous conditions (390-459, 470-8,

490-6, and all causes not elsewhere classified)

The overall exogenous and endogenous death rates for the three income areas, by broad age category, are shown in Table IV.3.2. As is conventional with cause-specific rates, the rates in the table are expressed in terms of 100,000 rather than 1,000 live births. Two conclusions are immediately suggested by these data. First, the vast majority of infant deaths today are caused by the endogenous conditions that are most closely associated with the physiological processes of gestation and birth. Second, both the exogenous and endogenous cause-specific death rates are inversely associated with family income. Not surprisingly, perhaps, the strength of the relationship, as measured by the difference between the death rates of the highest and lowest areas, is much greater for the environmentally related exogenous causes such as infections, accidents, and poisonings. The exogenous death rate in Area III is nearly three times greater than that in Area I. By contrast,

Table IV.3.2. Infant mortality rates (per 100,000 live births) by broad cause-of-death group for income areas in metropolitan Ohio, 1979-81

Income area

Exogenous causes

Endogenous causes







All areas







I (high)







II (medium)







III (low)







Source: Stockwell, Swanson, and Wicks (1986, 87-93).

Source: Stockwell, Swanson, and Wicks (1986, 87-93).

the Area III endogenous death rate is only twice as great as that of Area I.

There is a tendency for the exogenous causes to account for an increasing proportion of total deaths as income decreases: 11 percent of the infant deaths in Area I compared with 16 percent in Area III were due to exogenous causes. Thus, it is clear that, despite the much lower absolute death rate, the increased risk of an infant dying as the economic status of its parents declines is relatively much greater from environmentally related exogenous causes than it is from endogenous causes. It is true that the inverse association between infant mortality and economic status seems largely due to conditions that can generally be regarded as amenable to societal control. However, this should not lead one to minimize the significance of a consistent and pronounced inverse relationship for those endogenous conditions less resistant to control, which account for the vast majority of infant deaths.

Inspection of the exogenous-endogenous rates for the neonatal and postneonatal ages reveals that the pronounced inverse association with economic status characterizes both of the causal groups for both segments of infant mortality. The more interesting point here, however, is perhaps the challenge these data pose to the traditional distinction between neonatal-endogenous as opposed to postneonatal-exogenous mortality. In the past, demographers and other epidemiological researchers have commonly used the neonatal and postneonatal death rates as proxies for endogenous and exogenous mortality (Bourgeois-Pichat 1952). Yet while the Ohio data show a clear preponderance of endogenous causes in the neonatal period (93 percent), they also reveal a preponderance of endogenous causes among postneonatal deaths (74 percent). The increasing importance of the endogenous causes in the latter period likely reflects the nature of the technological progress made in recent years in enhancing the surviv ability of high-risk births. In other words, many infants who a generation ago would have died within a few days or weeks after birth now have a much greater chance of surviving. For some, this change will mean a chance to survive infancy and grow to adulthood leading relatively normal lives. For others, however, it will mean surviving the neonatal period only to succumb later in infancy; the frequency of deaths due to endogenous causes in the postneonatal period thus increases (Miller 1985). In any case, these findings indicate that there is no longer any basis for assuming an age-cause proxy relationship in infancy such as may have existed in the past (Stockwell, Swanson, and Wicks 1987).

Our results demonstrated that the same general conclusions apply to both sexes as well as to the two racial groups: Endogenous causes clearly predominate in all categories, and both cause-specific rates are inversely related to income status for all sex-color groups (Stockwell, Swanson, and Wicks 1988). Moreover, this pattern was also strongly apparent in those few instances where the numbers were sufficiently large to permit a comparison based on more specific causes of death (Stockwell et al. 1988).

Overall, the results of our research show that the basic inverse relationship between infant mortality and socioeconomic status cannot be attributed solely, or even largely, to either group of causes. Although more deaths are due to endogenous than to exogenous causes, and more deaths occur in the neonatal period regardless of cause, the variations in the death rates for both broad cause groups are characterized by a similar marked inverse differential for all major subgroups in the society.

Pregnancy And Childbirth

Pregnancy And Childbirth

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