Unequal and Uneven: The Geography of Higher Education Access
The school concentration index (SCI) is a new tool that measures local concentration in higher education markets. Using driving distances and school enrollment data across all higher education institutional types except advanced degrees, this interactive map visualizes this concentration by zip code tabulation area. (Zip code tabulation areas are areal representations of the more familiar USPS ZIP code service areas; we use the short form “zip” here for ease of reading.) The SCI ranges from 0, indicating perfect competition, to 10,000, indicating that one school accounts for all the enrollment for that zip; on the map, this range is visualized as green (perfect competition) to dark red (single monopolist). Zips that are maroon in color indicate an education desert—no higher ed nearby. Dark maroon areas are those with no associated zip—areas with no residents, like national parks or bodies of water.
As you explore the map, note that the DOJ and FTC use similar indices to measure market concentration in all types of markets. According to their benchmarks, a highly concentrated market scores above 2500 on the scale.
This map is the first in a series of publications examining market power in the US higher education system, and its effects on cost, access, indebtedness, and earning power. To read an explanatory blog post introducing and contextualizing the map and methodology, click here.
Methodology
The academic year represented here is 2016 - 2017. For more information on the implications of the map and our preliminary findings, read our report here. Below, find explanations of all variables. Email us with questions about methods and findings here.
Variables derived for each ZCTA:
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School Concentration Index (SCI) - We modeled the calculation of the SCI based on the Herfindahl-Hirschman Index (HHI). The HHI calculates market share for a particular company within a particular market; we calculate enrollment share for a particular school in a particular zip code tabulation area SCI ranges from 0 (perfect competition) to 10,000 (complete monopoly). A SCI of 10,000 indicates one school accounts for all the enrollment for that ZCTA.
$$ \text{SCI}_{\text{ZCTA}} = s_1^2 + s_2^2 + \dots + s_n^2 $$
Every ZCTA has a unique School Concentration Index where $n$ number of schools in each SCI equals the amount of schools where it is possible to drive to the associated ZCTA within 30, 45, or 60 minutes, depending on the selected map view. Each $s_n$ is the undergraduate enrollment share of a school within the geographic area, expressed as a whole number rather than a fraction.
- Number of Schools - The number of schools displayed for each ZCTA is a tally of the schools considered within a 30, 45, or 60 minute drive from at least a subsection of the ZCTA. Number of schools variable takes a whole number.
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Enrollment - The enrollment displayed for each ZCTA is the summation of the enrollment for every school considered within a 30, 45, or 60 minute drive from at least a subsection of the ZCTA. Enrollment variable takes a whole number and is sourced from IPEDS 12-Month Enrollment Table. This number indicates how many unduplicated undergraduate individuals enrolled for credit the institution served over a 12 month period, regardless of when the individual enrolled.
$$ \text{Enrollment}_{\text{ZCTA}} = \text{enrollment}_1 + \text{enrollment}_2 + \dots + \text{enrollment}_n $$
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25 Mile Zone Population Estimate - In place of population estimates for individual ZCTA, we list the summation of all the population estimates for the ZCTAs within 25 miles of the selected area; the purpose being to complement the zone-type scale used for the SCI. The 25 mile population zone originates from the mathematical centroid of each ZCTA.
$$ \text{Pop}_{\text{ZCTA-ZONE}} = \text{pop}_1 + \text{pop}_2 + \dots + \text{pop}_n $$
Every ZCTA has a unique 25 Mile Zone Population Estimate where $n$ number of ZCTAs in each ZCTA-zone equals the ZCTAs accessible to the root ZCTA within 25 miles. Each $\text{pop}_n$ is the 5-year population estimate for that specific ZCTA. Both $\text{pop}_n$ and $\text{Pop}_{\text{ZCTA-ZONE}}$ take a whole number.
Clear-cut variables per ZCTA:
- Zip Code Tabulation Area - (Via the US Census Bureau) ZCTAs are generalized areal representations of United States Postal Service ZIP Code service areas.
- Institution Name - These names are sourced from the IPEDS Institutional Characteristics table. It represents the Institution or Entity Name.
- Level of Institution - Level of Institutions are sourced from the IPEDS Institutional Characteristics table. A classification of whether an institution’s programs are 4-year or higher (4 year aka Bachelors), 2-but-less-than 4-year (2 year aka Associates), or less than 2-years (aka Below Associate).
- Control of Institution - Control of Institutions and definitions are sourced from the IPEDS Institutional Characteristics table. A classification of whether an institution is operated by publicly elected or appointed officials or by privately elected or appointed officials and derives its major source of funds from private sources.
- Public institution - An educational institution whose programs and activities are operated by publicly elected or appointed school officials and which is supported primarily by public funds.
- Private not-for-profit institution - A private institution in which the individual(s) or agency in control receives no compensation, other than wages, rent, or other expenses for the assumption of risk. These include both independent not-for-profit schools and those affiliated with a religious organization.
- Private for-profit institution - A private institution in which the individual(s) or agency in control receives compensation other than wages, rent, or other expenses for the assumption of risk.
- Population Estimate - Estimate; American Community Survey 5-year Estimates for the Total Population of the ZCTA. Data are based on a sample and are subject to sampling variability. Population Estimates for US Territories besides Puerto Rico are only available with the Census Bureau’s 2010 Census Data and only at the State Level. Used to create the 25 Mile Zone Population Estimate.
- Median Income Estimate - Estimate; Median household income in the past 12 months (in 2016 inflation-adjusted dollars) from American Community Survey 2012 - 2016 5-year estimates. If a ZCTA does not have a Median Income listed, this indicates that either no sample observations or too few sample observations were available to compute an estimate. For example, most US Territories do not have median income information.
Exclusion Criteria:
- We excluded schools that offered exclusively advanced degrees, exclusively distance learning degrees, and schools where level and control of institution were unknown. Also excluded were administrative offices of institutions when the institution itself was counted separately. For public schools, driving distances were restricted to the state where the school was located. If a school offered a bachelors or higher degree but no degree below bachelors and the undergraduate enrollment was below 100, the school was excluded.
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According to the IPEDS handbook,
All institutions in the U.S. and other U.S. jurisdictions that have a Program Participation Agreement (PPA) with the U.S. Department of Education to participate in Title IV federal student financial aid programs are required to report data to IPEDS, and are listed as separate entities in IPEDS. These entities are considered the "main campus."
Additionally,
- The IPEDS definition of a branch campus is "a campus or site of an educational institution that is not temporary, is located in a community beyond a reasonable commuting distance from its parent institution, and offers full programs of study, not just courses."
- The main campus and each additional location on the PPA are listed separately in IPEDS, and report their own data.
- The main campus reports combined data for itself and any additional locations that are not listed separately in IPEDS.
- Additional locations that are not listed separately have the option of being made "campuses" in IPEDS; a small number of data items are reported for each of these locations, and they are searchable in College Navigator.
About Our Researchers
This project was produced by the Higher Education Finance Team at Jain Family Institute. Principal researchers were Laura Beamer and Francis Tseng, with additional research from Ben Weintraut, Jack Gross, Maya Adereth, and Marshall Steinbaum.
About Our Sources
This analysis uses school-reported data from the final data release of 2016-17 Integrated Postsecondary Education Data System (IPEDS), 12-month enrollment data from the Provisional 2017 IPEDS database which lists enrollment for the previous academic year, 2016 5-year population and median income estimates from the American Community Survey, school isochrone creation from OpenStreetMap, and mapping abilities from MapBox and the US Census Bureau’s 2018 TIGER/Line Shapefiles.
