Simple Analysis of Birth Weight and Infant Mortality




Birth-weight distributions appear to be heterogeneous and composed of a primary subpopulation and a secondary subpopulation. These may be interpreted as the “normal” subpopulation and the “compromised” subpopulation. The secondary subpopulation accounts for the heavy upper and lower tails of the overall birth weight distribution.
See Figure 1.

    figure1

    Figure 1

The primary (dashed curves) and secondary (dash-dot curves) subpopulation densities for African American (bold curves) and European American (light curves) males. The results for females are similar.

The secondary subpopulation has lower infant mortality at every birth weight compared to the primary subpopulation. This may be attributed to selection due to differential fetal loss. See Figure 2.

    figure2

    Figure 2

The primary (dashed curves) and secondary (dash-dot curves) subpopulation-specific infant mortality for African American (bold curves) and European American (light curves) males. The results for females are similar.

Comparisons of African American and European American infant mortality indicate that primary mortality is higher among African American births, whereas secondary mortality is lower among African American births, probably because of heavier fetal loss among African Americans. See Figure 2.

The pediatric paradox is due to the significantly lower secondary mortality at the lower birth weights and the higher proportion of secondary births among African Americans. See Figure 3.

    figure3

    Figure 3

The total birth-weight-specific infant mortality for African American (bold curves) and European American (light curves) males. The confidence intervals are shown as dashed (African American) and dotted (European American) lines.  

These results suggest that the health differential between African Americans and European Americans, are significantly underestimated using the standard methods.

     

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