IJE Advance Access originally published online on April 28, 2005
International Journal of Epidemiology 2005 34(4):888-895; doi:10.1093/ije/dyi092
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Published by Oxford University Press 2005
Social Inequalities |
Contextual effect of income inequality on birth outcomes
1 National Center for Health Statistics, Hyattsville, MD 20782, USA
2 Department of Epidemiology, University of Michigan, Ann Arbor, MI, USA
* Corresponding author. Office of Analysis and Epidemiology, Rm 6112, 3311 Toledo Road, Hyattsville, MD 20782, USA. E-mail: mhuynh{at}cdc.gov
Background Though associations between income inequality and birth outcome have been suggested, mechanisms underlying this relationship are not known. In this analysis, we examined the relationship between income inequality and preterm birth (PTB) and post-neonatal mortality (PNM) to explore two potential mechanisms—the proposed psychosocial stress and neo-material pathways.
Methods Data on singleton births from 1998 to 2000 were obtained from the CDC's National Center for Health Statistics' Linked Birth and Infant Death files. The Gini Index was utilized to measure income inequality and was divided into tertiles representing high, medium, and low county-level inequality. To determine the association between the birth outcomes and county income inequality and to account for clustering within counties, we employed generalized estimating equation (GEE) modelling.
Results PTB increased from 8.3% in counties with low income inequality to 10.0% in counties with high inequality. The Gini Index remained modestly associated with PTB after adjusting for individual level variables and mean county-level per capita income within the total population (AOR: 1.06; 95% CI 1.03–1.09) as well as within most of the racial/ethnic groups. PNM increased from 1.15 deaths per 1000 live births in low inequality counties to 1.32 in high-inequality counties. However, after adjustment, income inequality was only associated with PNM within the non-Hispanic black population (AOR: 1.20; 95% CI 1.03–1.39).
Conclusions These findings may provide some support for the association between income inequality and PTB. Further research is required to elucidate the biological mechanisms of income inequality.
Keywords Income inequality, Gini coefficient, preterm birth, post-neonatal mortality
Accepted 5 April 2005
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