In order to better understand the statistical relationship between measures of birthweight and gestational age and their effects on infant mortality, national vital statistics data was examined using non-parametric regression techniques (GAM) that allow for a sophisticated and detailed analysis of infant mortality models. These models allow for various non-linear effects of birthweight and gestational age on infant mortality to be quantified based upon extant methodologies (Solis, Pullum and Frisbie, 2000). Utilizing over-time, race/ethnicand sex-specific approaches, the identification of "zones" of optimal birth outcomes based upon infant mortality probabilities is successfully accomplished. This process results from the creation of a rigorous cross-classification of GAMsupplied birthweight and gestational age parameters. From these results, I find that Non-Hispanic Black infants still exhibit an infant mortality disadvantage relative to Non-Hispanic Whites and Mexican American infants. For the four birth outcome parameters and their interactions, I find evidence of infant mortality disadvantage for infants that are early or late as well as small or heavy relative to their race/ethnic-specific, birthweight-adjusted optima.

The objective of this study was to examine if intra-racial income inequality contributes to higher infant mortality rates (IMRs) for African-Americans. The conceptual framework for this study is derived from Richard Wilkinson's psychosocial environment interpretation of the income inequality and health link. The hypotheses examined were that race/ethnicity-specific IMRs are influenced by intra-race/ethnicity income inequality, and that these effects of income inequality on health are mediated by level of social mistrust and/or risk profile of the mother. Using state-level data from several sources, the 2000 National Center for Health Statistics Linked Birth Infant Death database, 2000 U.S. Census, and 2000 General Social Survey, a number of regression equations were estimated. Results indicated that the level of intra-racial/ethnic income inequality is a significant predictor of non-Hispanic Black IMRs, but not the IMRs of non-Hispanic Whites or Hispanics. Additionally, among Blacks, the effect of their intra-racial income inequality on their IMRs was found to be mediated by the risk profile of the mother, namely, the increased likelihood of smoking and/or drinking and/or less prenatal care by Black women during pregnancy. Implications of the findings are discussed.