PolicyLink and PERE
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An Equity Profile of Orange County
Measures of diversity and segregation
In the equity profile, we refer to a measure of
racial/ethnic diversity (the "diversity score"
on page 21) and several measures of
residential segregation by race/ethnicity (the
"multi-group entropy index" on page 74 and
the "dissimilarity index" on page 75). While
the common interpretation of these measures
is included in the text of the profile, the data
used to calculate them, and the sources of the
specific formulas that were applied, are
described below.
All of these measures are based on census-
tract-level data for 1980, 1990, and 2000
from Geolytics, and for 2016 (which reflect
the 2012 through 2016 average) from the
2016 5-year ACS. While the data for 1980,
1990, and 2000 originate from the decennial
censuses of each year, an advantage of the
Geolytics data we use is that it has been "re-
shaped" to be expressed in 2010 census tract
boundaries, and so the underlying geography
for our calculations is consistent over time;
the census tract boundaries of the original
decennial census data change with each
release, which could potentially cause a
Data and methods
change in the value of residential segregation
indices even if no actual change in residential
segregation occurred. In addition, while most
all the racial/ethnic categories for which
indices are calculated are consistent with all
other analyses presented in this profile, there
is one exception. Given limitations of the
tract-level data released in the 1980 Census,
Native Americans are combined with Asian
Americans/Pacific Islanders in that year. For
this reason, we set 1990 as the base year
(rather than 1980) in the chart on page 75,
but keep the 1980 data in other analyses of
residential segregation as this minor
inconsistency in the data is not likely to affect
the analyses.
The formulas for the diversity score and the
multi-group entropy index were drawn from a
2004 report by John Iceland of the University
of Maryland, The Multigroup Entropy Index
(Also Known as Theil's H or the Information
Theory Index) available at:
https://www.census.gov/topics/housing/hous
ing-patterns/about/multi-group-entropy-
index.html. In that report, the formula used to
calculate the Diversity Score (referred to as
the "entropy score" in the report) appears on
page 7, while the formulas used to calculate
the multigroup entropy index (referred to as
the "entropy index" in the report) appear on
page 8.
The formula for the other measure of
residential segregation, the dissimilarity
index, is well established, and is made
available by the U.S. Census Bureau at:
https://www.census.gov/library/publications/
2002/dec/censr-3.html.
