Estimates And Projections Area Methodology
State Population Estimates By Age, Sex, Race, And Hispanic Origin For
July 1, 2005
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Version of this methodology
The U.S. Census Bureau produces
estimates of the resident population by age, sex, race, and Hispanic origin for
each state in the United States and the District of Columbia on an annual
basis. The following documentation outlines the methods that were used in the
production of the July 1, 2005 estimates.
OVERVIEW
For the July 1, 2005 state
estimates of the resident population by age, sex, race, and Hispanic origin,
the Census Bureau used a distributive cohort component method. This method was
applied in the following manner. First, we started with previously developed
resident state population estimates by age and sex and resident national
population estimates by age, sex, race, and Hispanic origin. Second, we
estimated the age, sex, race, and Hispanic origin distributions for each state
by estimating post-censal change in the corresponding populations with a cohort
component model. Third, we applied these distributions to the original state
age-sex and national characteristics estimates. A detailed discussion of this method
is provided below.
Estimating the Race and Hispanic Origin Distributions
The majority of the work that went
into producing the state resident population estimates by age, sex, race, and
Hispanic origin consisted of estimating the race and Hispanic origin
distributions for each state-age-sex estimate. This was done by producing a
preliminary set of age, sex, race, and Hispanic origin estimates for each state
and then calculating the race-Hispanic origin proportions from these.
The preliminary set of resident population estimates by age,
sex, race, and Hispanic origin was produced by first splitting the Census
population into two mutually exclusive universes: The household population and
the group quarters (GQ) population. For the household population, a cohort
component technique was then used to estimate change in this population. For
the GQ population, GQ change was estimated through a data-collection effort
conducted in conjunction with members of the Federal State Cooperative Program
of Population Estimates (FSCPE). The resulting household and GQ estimates were
then added together to produce the new set of preliminary resident population
estimates
The Preliminary Household Population Estimates
The cohort-component technique used
to estimate the household population follows each birth cohort across time
according to its exposure to mortality, fertility, and migration. This
technique was applied using the following equation.
P1 = P0 + B - D + NDM + NIM + NMM
Where:
P1 = population at the end of the
period
P0 = population at the beginning of
the period
B = births during the period
D = deaths during the period
NDM = net domestic migration during
the period
NIM = net international migration
during the period
NMM = net military movement during
the period
The actual application of this
algorithm was quite simple. Not so simple was the preparation of the input
data. Great care was taken to estimate each component of this equation as
accurately as possible. The details of this work are outlined below.
One complicating factor in the
estimation of the household population was that the administrative data used in
these estimates continues to come to the Census Bureau with different race
categories than used in Census 2000. In Census 2000, information was gathered using
6 races groups (White; Black; American Indian and Alaska Native; Asian; Native
Hawaiian and Pacific Islander; and Some Other Race). In addition, individuals
were allowed to report multiple races. Conversely, most administrative data
available for the estimates still come to us in the 4 race categories
consistent with the 1990 census (White; Black; American Indian, Eskimo, or
Aleut; and Asian and Pacific Islander). For this reason, the household
estimates were processed with the 4 race categories consistent with the 1990
census and the results were converted to race categories consistent with Census
2000. Details of all the conversions needed in order to carry out this
procedure are presented below.
1.
Specification of the Base Population
The enumerated population from Census 2000 was the
base for the July 1, 2005 estimates. This population was modified in four ways
to prepare it for inclusion in the cohort-component technique.
- The original race
data from the Census were modified to eliminate the "some other
race" category.1
- The April 1, 2000
population estimates base reflects modifications to the Census 2000
population as documented in the Count Question Resolution program and
errata notes.2
- The Census 2000 base
household population was converted from the 31 race categories to the
four race groups consistent with the 1990 Census by "straight
proportional allocation."
- Finally, the results
of step [c] were used to estimate the population on July 1, 2000.3
This was done as follows:
- A set of
race-Hispanic origin proportions was calculated by summing the data by
state, age, and sex and then dividing each state-age-sex-race-origin
cell by the corresponding sum.
- These proportions
were then applied to the previously produced state age-sex estimates
for July 1, 2000.
- Finally, the results
were controlled to the July 1, 2000 national estimates by age, sex,
race, and Hispanic origin.
2.
Specification of Births
The birth component was calculated with data from
two sources. The Federal State Cooperative Program for Population Estimates
(FSCPE) provided data on all registered births that occurred in the members'
respective state for calendar years 2000-2004. The FSCPE births were adjusted
and distributed by sex, race (consistent with the 1990 Census), and Hispanic origin
using data from The National Center for Health Statistics (NCHS). Finally, data
for the last 6 months of the estimate period (January 1 - June 30, 2005) were
assumed to be equal to the number of births from July 1 - December 31, 2004.
These final birth counts were considered to be complete for the resident
population. No adjustments were made for under coverage or differential
coverage by state, sex, race, or Hispanic origin.
3.
Specification of Deaths
The death component was also calculated with data
from two sources. The Federal State Cooperative Program for Population
Estimates (FSCPE) provided data on all registered deaths that occurred in the
members' respective state for calendar years 2000-2004. The FSCPE deaths were
adjusted and distributed by age, sex, race (consistent with the 1990 Census),
and Hispanic origin using data from The National Center for Health Statistics
(NCHS). Finally, data for the last 6 months of the estimate period (January 1 -
June 30, 2005) were assumed to be equal to the number of deaths from July 1 -
December 31, 2004. These final death counts were considered to be complete for
the resident population. No adjustments were made for under coverage or
differential coverage by state, age, sex, race, or Hispanic origin.
4.
Specification of Net International Migration
The net international migration component consisted
of three migration flows: (1) net migration of the foreign-born, (2) emigration
of natives, and (3) net movement from Puerto Rico to the United States.
To measure the net migration of the foreign born,
we used the American Community Survey (ACS) because it provided annually
updated data. We first determined the national level of migration for the
foreign born by calculating the net difference in the estimates of these surveys
from 2000 to 2001, 2001 to 2002, 2002 to 2003, and 2003 to 2004. We then
accounted for deaths to the entire foreign-born population during the periods
of interest to arrive at the final national estimate of net migration of the
foreign born. In order to account for variability due to small sample sizes of
the foreign born, we used a moving average for the period changes to get the
final net foreign-born migration estimate. Then, to ascribe county of
destination, age, sex, race, and Hispanic origin to these estimates, we applied
the distribution of the non-citizen foreign born from Census 2000 who entered
in 1995 or later to the national-level estimate. Finally, we assumed the net
migration of the foreign born between 2004 and 2005 to be the same as net migration
between 2003 and 2004.
The national net movement from Puerto Rico to the
United States by age and sex was measured using levels observed during the
1990s.4 To assign characteristics to these flows, we applied the
age-sex-race-Hispanic origin-destination county distributions from Census 2000
from those who indicated that their place of birth was Puerto Rico and who had
entered the United States in 1995 or later.
The emigration of natives was produced in a similar
way to the net movement from Puerto Rico. Again, the national levels of
movement were measured using levels observed during the 1990s.5
Then, to assign characteristics to these flows, we applied the
age-sex-race-Hispanic origin-destination state distributions from Census 2000
of all natives who currently reside in the United States. Therefore, the
characteristics of natives who emigrated were assumed to be the same
age-sex-race Hispanic origin-destination state distribution as natives residing
in the 50 states and the District of Columbia in Census 2000.
Once the net migration of the foreign born, net
movement from Puerto Rico, and the emigration of natives were estimated, all
three parts were combined to estimate a final net international migration
component.
5.
Specification of Net Internal Migration
For the July 1, 2005 estimates, internal migration
was estimated using data from two administrative record sources: annual
individual-level extracts of tax returns provided by the Internal Revenue
Service (IRS); and the Census Numident file derived from the Social Security
Administration 100 percent file (SSA).
The IRS 1040 tax return records were matched to the
SSA data to identify the age, sex, race, and Hispanic origin of the tax filers.
Next, demographic characteristics were assigned to spouses and dependents of
each filer using several simplifying assumptions. First, spouses were assigned
the same age and the opposite sex as filers. Second, exemptions claimed for
dependent children were assigned to the under-20 age group and exemptions claimed
for dependent parents were assigned to the 65 and over age group. Third, the
sex of dependent children and parents was assigned randomly. Fourth, the spouse
and other dependents were assigned the same race and Hispanic origin as the
filer.
After the demographic characteristics were assigned
to the IRS tax return records, two years of records were matched and a
migration status was assigned. Filers and their dependents with a change in the
state of residence between the two periods were identified as "inter-state
migrants." If there was no change in the state of residence, the filers and
dependents were identified as non-migrants.
It was now possible to calculate both the
out-migration rates and in-migration proportions for each state by age, sex,
race, and Hispanic origin. First, the out migration rate for each age, sex,
race, and Hispanic origin group within a state was computed by dividing the
number of "inter-state migrants" moving out of the state during the period
by the number of filers and dependents (i.e., exemptions) in the state at the
beginning of the period.6 Then, to calculate the in-proportions for
the age, sex, race, and Hispanic origin groups of each state, the out-migration
rates were multiplied by a proxy estimate of the population for that year taken
from the previous vintage of estimates (vintage 2004). From this, the
inter-state in-migration proportion for each state was calculated by dividing
the number of in-migrants by age, sex, race, and Hispanic origin for that state
by the national sum for that characteristic group.
In the production of the out-migration rates and
in-migration proportions, when the number of exemptions for any
age-sex-race-Hispanic origin category (which will be referred to as a cell) was
low, the exemptions were combined with those of other cells in order to improve
the robustness of the resulting migration out-rates or in-proportions. If a
given cell had less than 30 exemptions, it was combined with the exemptions of
adjacent age cells within the same sex-race-Hispanic origin group until the
combined category contained at least 30 exemptions. If it was not possible to
create a combined category containing at least 30 exemptions with the
procedure, then cells were combined for both sexes. After this was done and the
out-migration rate or in-migration proportion was calculated, each of the
individual ages was assigned the rate or proportion of the aggregated age
group.
Two other aspects of the estimation of the
out-migration rates and in-migration proportions should be noted. First, the
individual ages in the 0-19 and 65+ age groups were assigned the same
out-migration rate or in-migration proportion as the aggregated age group.
Second, the age distributions of the out-migration rates and in-migration
proportions by state, sex, race, and Hispanic origin were smoothed using a
moving average.
The final step in the production of the number of in- and
out-migrants for each state occurred during the actual estimation process. The
out-rates are applied to the estimate of the population at the beginning of the
period to generate the number of state out migrants by age, sex, race, and
Hispanic origin. Then, these migrants are converted into in-migrants for each
state by age, sex, race, and Hispanic origin by multiplying the in-proportions
for each state by the corresponding national sums.
6.
Specification of Net Military Movement
The net movement of the military, both foreign and
domestic, into each state for each year was estimated using data received
directly from the armed forces and the Department of Defense. They provided
yearly estimates of the station strength in each state from 2000 to 2005. The
net-movement was then calculated as the difference in the station strength from
one year to the next. Finally, the age, sex, race, and Hispanic origin
distribution was assigned using those who reported being employed by the
military in Census 2000.
The Preliminary GQ Population Estimates
Group Quarters (GQ) population
change is estimated separately from the household population because of the
unique character of this subpopulation and the ability to acquire direct data
that reflects change in this population. The technique for estimating the GQ
population for the vintage 2005 estimates started with the Census 2000
enumerated GQ population. As with the household population, the race breakdowns
of the GQ data were converted from categories consistent with Census 2000 to
categories consistent with 1990 through proportional allocation (see above).
Next, the state representatives who
participate in the Federal-State Cooperative Program for Population Estimates
(FSCPE) developed an independent list of GQ facilities in their state with the
populations typically associated with them at the time of Census 2000 and
annually from 2000 to 2005 from the sources available to them in their state.
In turn, the Census Bureau calculated the implied change in the GQ population
from the numbers provided by the FSCPE members. This change was then applied to
the Census GQ base to come up with the estimate of the total GQ population in
the state. Finally, these state totals were distributed by age, sex, race, and
Hispanic origin using the distribution of the GQ population within each GQ type
from the base GQ population.
The Final Population Estimates by Demographic Characteristic
The final steps in the production
of the vintage 2004 state characteristics estimates consisted of 1) adding
together the household and GQ population estimates for each year, 2)
calculating the necessary proportions from the preliminary estimates and
applying them to both the previously created state population estimates by age
and sex and the National estimates by age, sex, race, and Hispanic origin, and
3) converting the data from the 4 race categories consistent with the 1990
census to the categories consistent with Census 2000.
In combining the household and GQ
population estimates, the only caveat that should be noted is that it was
assumed that there was no change to the GQ population between April 1, 2000 and
July 1, 2000.
The next step in the production of
the state estimates by age, sex, race, and Hispanic origin was to control the
preliminary resident state estimates by age, sex, race, and Hispanic origin to
both the previously created resident state population estimates by age and sex
and the national resident estimates by age, sex, race, and Hispanic origin.
This was done through a two-step iterative process.
In the first step, the preliminary
state characteristic estimates were summed to the national level by age, sex,
race, and Hispanic origin. Next, proportions were calculated by dividing each
state-age-sex-race-Hispanic origin cell by the corresponding sum. Finally,
these proportions were applied to the original national characteristics
estimates in order to calculate an intermediate set of state estimates by age,
sex, race, and Hispanic origin.
In the second step, a similar
procedure was used to calculate new proportions from the transformed data so
that the state age-sex estimates could be distributed by race and Hispanic origin.
First, the preliminary state characteristic estimates were summed to the state
level by age and sex. Next, proportions were calculated by dividing each
state-age-sex-race-Hispanic origin cell by the corresponding sum. Finally,
these proportions were applied to the original state age-sex estimates in order
to calculate an intermediate set of state estimates by age, sex, race, and
Hispanic origin.
When attempting to make estimates
consistent with two different sets of data using the procedure described above,
performing the second step of the iteration tends to distort the fit achieved
in the first step. Likewise, repeating the first step again tends to distort
the fit achieved in the second step. However, these distortions can be
minimized by repeating the two-step procedure multiple times. For this reason,
the iterative procedure was repeated five times. After this, the resulting set
of estimates was rounded to integers.
The final step in the estimates
process was to convert the estimates from the 4-race categories consistent with
the 1990 census in which the estimates were processed to the 31-race categories
consistent with Census 2000. To do this, the procedure used to go from 31 to 4
races was essentially reversed. First, the proportion of each 4-race category
associated with the 31 race categories was calculated for both universes using
Census 2000 household and GQ data by state, age, sex, and Hispanic origin.
Next, the GQ population for each estimate year was subtracted from the
corresponding resident population in order to arrive at the household
population for that estimate year. Then, the proportions for both the household
and GQ data were applied to the respective 4-race estimates for each year to
arrive at the 31-category race household and GQ estimates.7 Finally,
the 31-category household and GQ estimates by age, sex, and Hispanic origin
were added together to arrive at the final resident state population estimates
by age, sex, race, and Hispanic origin.
1 This
modification has been accepted for all Census Bureau estimates products and is
explained in the document entitled "Modified Race Data Summary File Technical
Documentation and ASCII Layout" that can be found on the Census Bureau website
at http://www.census.gov/popest/archives/files/MRSF-01-US1.html.
2 Details about the
Count Question Resolution Program can be found on the Census Bureau website at http://www.census.gov/dmd/www/CQR.htm.
Errata notes can be found on the Census Bureau website at http://www.census.gov/prod/cen2000/notes/errata.pdf.
3This step was needed
since the estimates procedure produces annual estimates and since the target
reference date for each estimate year is July 1.
4 A description of the
methodology used to produce these estimates can be found on the Census Bureau
website at http://www.census.gov/population/www/documentation/twps0064.html.
5 A description of the
methodology used to produce these estimates can be found on the Census Bureau
website at http://www.census.gov/population/www/documentation/twps0063.html.
6 Technically, the
quotient produced by this procedure is the probability of moving out of the
state. However, we make the simplifying assumption that the out-migration rate
is the same as the probability of moving out of the state.
7 The reason for
separating the process of converting the household and GQ data from 4 to 31 races
is that the GQ data are processed by GQ type so that they may be used in
estimates not described in this document. |
