The graphs below show the difference in percentage change of income growth between the richest D.C.-area counties and the rest of the United States:
The differences in income growth, using these two measures, are clear. The D.C. area has gotten fatter, especially the richest counties.
In addition to the public relations and lobbying boom Glenn mentions as one factor influencing the region’s wealth, total federal spending is likely another influencing factor. Income growth rates in the richest D.C.-area counties (and Washington itself) are approximately twice those for the rest of the country; the D.C.-area growth rates are 10% higher than the richest non-D.C.-area counties.
The percentage of total federal government spending growth for 2000 to 2010 corresponds closely to the percentage growth in median incomes in the D.C. area’s richest counties compared to the rest of the United States: it also approximately doubles, from around $1.8 trillion in 2000 to around $3.5 trillion in 2010. Total federal spending is certainly not the only indicator of income growth in the Washington region, but there appears to be a relationship.
I used two different measures of income from the U.S. Census:
Median Household Income: “Income of the householder and all other individuals 15 years old and over in the household, whether they are related to the householder or not”.
Median Family Income: The total income of a family, as defined by the Census: “A family consists of two or more people (one of whom is the householder) related by birth, marriage, or adoption residing in the same housing unit.” This definition is more likely to have a dual-income household.