Technical Information
Identification
of black and white subgroups
The Census
offers two ways to identify a person's geographic origin: ancestry and
country of birth. We identify geographic origin by ancestry. Where ancestry
is not available, we use country of birth.
Census respondents
were able to list a first and second ancestry. To avoid double-counting,
we use only the first ancestry here. A large majority of each ethnic group,
identified by either first or second ancestry, is captured this way. For
users interested in one specific group, it may be preferable to use both,
which would yield a larger group size.
American ancestry
includes all people identifying their ancestry as American or United States.
European
ethnic groups are identified solely by first ancestry.
Most Muslim-origin
groups are also identified by first ancestry. Among the ancestries
included in North African are Ethiopian and Sudanese. Although Ethiopia
and Sudan are actually sub-Saharian African countries, they are included
in the Muslim-origin category because they have a Muslim majority. But
some important origins are not identifiable in Census summary files. For
these groups, we rely on country of birth, which has the disadvantage
of capturing only the first generation. These include people from Afghanistan,
Indonesia, Malaysia and Pakistan, who are identified as South Asian in
our data tables.
Among blacks,
the best method of identifying Afro-Caribbeans is by first ancestry. The
count of Africans, however, would be inflated by using ancestry, because
many blacks who are descended from several generations of forebears in
the U.S. list their ancestry as African. Therefore, we again rely on country
of birth for this group, with the accompanying disadvantage of counting
only the first generation.
In some other census
sources, such as the Current Population Survey (CPS), parents' countries
of birth are also reported. National estimates of groups' population size
that include both the first and second generations can be compared to
the figures in these web pages. However the sample size of the CPS is
insufficient to be a basis of estimates of group populations in most metro
areas.
Comparing black
ethnic total to non-Hispanic black total
The black-origin total
is computed by summing the total number of Afro-Caribbeans, African, and
African-Americans in a given metro area. Although each of the black-origin
categories is comprised of non-Hispanic individuals, often the black-origin
total will not match the non-Hispanic black total in a given area. In
most cases the difference in values will be negligible, but we have identified
two potential sources for the observed discrepancies:
1. While the Census
provides data for ancestry and place of birth (used to construct the Afro-Caribbean
and sub-Saharan African categories, respectively), these variables are
not available by race. As a consequence, a small number of whites are
represented in our Afro-Caribbean and African totals.
2.The ancestry and nativity classifications are not mutually exclusive.
It is possible for an individual to be born, for example, in sub-Saharan
Africa and to be of Afro-Caribbean ancestry. In such cases individuals
will be represented twice in our black-origin total (once as Afro-Caribbean
and once as African). Such cases are admittedly rare, but it is impossible
to derive a precise estimate using currently available 2000 census data.
However, the 1990 IPUMS data show that such cases comprised only .32%
of the nationwide sample.
Metropolitan Statistical
Areas
The data on
our pages are reported for metropolitan regions. The Census Bureau uses
a standard set of definitions of the area included in each "metropolitan
statistical area" (MSA) or "primary metropolitan statistical
area" (PMSA). In most cases both a central city (or sometimes two
or more central cities) and the ring of surrounding suburbs are included.
At the top of the page for each metro area, we have listed the counties
and the city (or cities) that the Census has designated as the central
city (or cities) for that area. After viewing data for the entire metropolitan
area, you may elect to see information for only the central city or suburban
portion. If there is more than one central city, please remember that
what we report is for all these cities combined.
Isolation Index
The isolation index
is the percentage of same-group population in the census tract where the
average member of a racial/ethnic group lives. It has a lower bound of
zero (for a very small group that is quite dispersed) to 100 (meaning
that group members are entirely isolated from other groups). It should
be kept in mind that this Index is affected by the size of the group --
it is almost inevitably smaller for smaller groups, and it is likely to
rise over time if the group becomes larger.
Exposure Index
The exposure indices
(P*) describes a group's exposure to all racial groups. We use it to determine
the racial composition of the neighborhood of the average person of a
given race. When we compare exposure indices for different parts of a
metro area (for example the suburbs) with the metro area as a whole, we
can see whether a racial group is evenly distributed across the neighborhoods
in the metropolitan area, or whether the group is concentrated in neighborhoods.
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