Income inequality

This indicator responds to growing attention, nationally and globally, to income inequality. High levels of inequality are correlated with, among other things, life expectancy, infant mortality, crime, and social instability (source: U.S. Census).

Chesapeake watershed region and county-level maps comparing income inequality scores.

How is it measured?

A standard measure of income inequality is the Gini Coefficient. Perfectly distributed income, with say 50% of the population having 50% of the income, has a Gini Coefficient of 0. The higher the Gini Coefficient (with a ceiling of 1), the higher the level of inequality. The U.S. Census five-year American Community Survey contains GINI Coefficient data at the county level. The data of the 197 counties that intersect the Chesapeake Bay watershed boundary are aggregated into regions, used to calculate a z-score, converted to a report card score, and then weighted by population. For the z-score, GINI Coefficient data are compared to the mean and standard deviation of the 197 Chesapeake Bay counties.

For the 2021 report card, data from 2019 was used. The mean of the Chesapeake Bay watershed income inequality was 0.434, and the standard deviation was 0.034.

Threshold Levels

To compare between the four economic indicators, we established a z-score lower and upper bounds (-2.5 to 2.5) that are used to translate a z-score to a 0–100 grading scale—the equation is y =  100 - (20x + 50) where y = the report card score and x = the z-score.