Finding Montgomery County's National Peers
Having meaningful points of comparison is a critical aspect of effective data analysis. For Montgomery County, the experiences of comparable jurisdictions provide a frame of reference for understanding our successes and challenges. To that end, in 2008 CountyStat sought to identify counties like our own to use as benchmarks and references for putting the characteristics of Montgomery County in a more meaningful context.
The most obvious peer jurisdictions are those that immediately border Montgomery County: Prince George’s, Howard, and Frederick Counties in Maryland, Loudoun and Fairfax Counties in Virginia, and the District of Columbia. These five counties and one city all share economic, cultural, and social characteristics that come from being in the National Capital Region. Although there is considerable variety within them, these neighboring jurisdictions provide a stable understanding of how Montgomery County stacks up within our regional community.
Besides our DC-area neighbors, CountyStat identified benchmark counties from all over the country that closely resemble the fundamental and unique attributes of Montgomery County. However, selecting these counties is a difficult and open-ended process that has gradually progressed over time.
At the outset, CountyStat used a mix of cutoffs and goodness-of-fit clustering to select benchmark counties. Looking among suburban counties with a county government system, we selected counties that had at least 75% of Montgomery County’s per capita income and ranked comparably among 10 economic and social indicators. Using this method, we identified 34 counties that fit our criteria, representing metropolitan areas from around the country.
Original national peer jurisdictions identified by CountyStat
After relying on this list for several years, however, we began to see considerable room for improvement. For instance, the original methodology rejected all counties with major urban areas inside of them, but as Montgomery County is home to Bethesda, Silver Spring, Rockville, and other heavily built up areas that resemble larger cities, we became more comfortable comparing ourselves with traditionally “urban” localities. The variables used to create the original list also skewed heavily toward economic characteristics over social ones, meaning that many of the original peer counties did not resemble the ethnic and international diversity that defines Montgomery County.
To remedy these issues, we introduced a new technique. Analyzing all US counties with a population of at least 100,000, we used a k-means clustering system to sort counties into like groups. This system was powered by a more balanced, streamlined list of five variables: median household income, population under 200% of the poverty line, foreign-born population, non-white population, and population with bachelor’s degrees.
This system matched us with 27 national peers, 20 of which were on our previous list. The selected counties clustered in a few major metropolitan areas, specifically DC, New York, Boston, and San Francisco, and included many jurisdictions once rejected as being too urban. These new jurisdictions replaced counties on the initial list that were less diverse and less well-off than Montgomery County.
Map of the 27 new national peer jurisdictions selected in August 2018
This process produced a list of benchmark counties that better match Montgomery County in more meaningful and useful ways, and you can see how we stack up against one another by visiting one of CountyStat’s Community Indicators data pages.