Decomposing Mortality Disparities in Urban and Rural U.S. Counties

Abstract

Objective: To understand the role of county characteristics in the growing divide between rural and urban mortality from 1980 to 2010.

Data source: Age-adjusted mortality rates for all U.S. counties from 1980 to 2010 were obtained from the CDC Compressed Mortality File and combined with county characteristics from the U.S. Census Bureau, the Area Health Resources File, and the Inter-University Consortium for Political and Social research.

Study design: We used Oaxaca-Blinder decomposition to assess the extent to which rural-urban mortality disparities are explained by observed county characteristics at each decade.

Principal findings: Decomposition shows that, at each decade, differences in rural/urban characteristics are sufficient to explain differences in mortality. Furthermore, starting in 1990, rural counties have significantly lower predicted mortality than urban counties when given identical county characteristics. We find changes in the effect of characteristics on mortality, not the characteristics themselves, drive the growing mortality divide.

Conclusions: Differences in economic and demographic characteristics between rural and urban counties largely explain the differences in age-adjusted mortality in any given year. Over time, the role these characteristics play in improving mortality has increased differentially for urban counties. As characteristics continue changing in importance as determinants of health, this divide may continue to widen.

Keywords: Econometrics; determinants of health; geographic/spatial factors; population health; rural health; small area variations; socioeconomic causes of health.

Figure 1

Age‐Adjusted Mortality Rate: Rural, Urban, and Rural Counterfactual

1. Notes. Dashed line represents predicted age‐adjusted mortality rate for a county with coefficients from urban regression estimates and average rural characteristics at each decade. Bars represented 95% confidence intervals generated through 500 bootstrapped replications of the prediction.

Figure 2

Predicted Change in Age‐Adjusted Mortality Rate by Category

1. Notes. Dashed line represents predicted age‐adjusted mortality rate for a county with coefficients from urban regression estimates and characteristics replaced with those of a rural county within each category. Demographic characteristics include racial and ethnic composition, foreign‐born population, and net migration rate. Economic characteristics include education, poverty, and unemployment. Geographic distribution is percent of counties in each census region. Bars represented 95% confidence intervals generated through 500 bootstrapped replications of the prediction.

Figure 3

Mortality Changes over Time Attributable to Characteristic Changes

1. Notes. Dashed lines represent separate urban/rural predictions where county characteristics change in each decade and regression coefficients remain at 1980 values. Bars represented 95% confidence intervals generated through 500 bootstrapped replications.