To determine the ZIP code with the smallest income gaps in every state, 24/7 Wall St. reviewed five-year estimates of the Gini Index of income inequality from the U.S. Census Bureau’s 2019 American Community Survey.
The Gini Index of income inequality summarizes income dispersion in an area on a scale from 0 to 1. A value of 0 indicates perfect equality — everyone in the area receives an equal share of income. A value of 1 indicates perfect inequality — only one recipient receives all the income.
We used ZIP Code Tabulation Areas — a census geography type which defines areal representations of United States Postal Service ZIP codes (USPS ZIP codes do not define geographic boundaries but instead are a network of mail delivery routes in a service area). We refer to Census ZCTAs as ZIP codes.
Of the 33,120 ZIP codes the Census publishes data for, 32,936 had boundaries that fell within one of the 50 states, while the rest were in the District of Columbia or Puerto Rico.
ZIP codes were excluded if the Gini Index was not available in the 2019 ACS, if there were fewer than 1,000 housing units, or if the sampling error associated with a ZIP code’s data was deemed too high.
The sampling error was defined as too high if the coefficient of variation — a statistical assessment of how reliable an estimate is — for a ZIP code’s Gini Index was above 15% and greater than two standard deviations above the mean CV for all ZIP codes’ Gini Indices. We similarly excluded ZIP codes that had a sampling error too high for their population, using the same definition.
The remaining 16,721 places were ranked within their state based on their Gini Index. To break ties, we used the share of aggregate household income earned by the top 20% of households.
Additional information on average household income by quintile, share of aggregate household income by quintile, and median household income are also five-year estimates from the 2019 ACS.
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