Census Background

Census: 100 Percent Count of Units

Survey: Sample of Units
Censuses

Decennial Census: Population and Housing

Economic Census: Business and Industry

Agriculture Census: Farms

Census of Government: Local and State
U.S. Census Bureau Surveys
http://www.census.gov/
Decennial Census Survey: Population and
Housing
 American Community Survey
 Current Population Survey
 Survey of Income Participation Programs
 American Housing Survey

International Program Center
Part of U.S. Census Bureau Population
Division
 Assist in Census data collection and
processing for countries throughout the
world
 http://www.census.gov/ipc/www/

Census of Population and Housing,
2000 (Short Form)

Seven Q’s
 Name
 Sex
 Age
 Relationship
to Householder
 Hispanic Origin
 Race (can chose multiple categories)
 Owner/Renter
Census 2000 Survey (Long Form)
Includes all Q’s on Short Form
 Densely populated sampling areas

 (1

Sampling areas less than 2,500 persons
 (1

in 8 HHs surveyed)
in 2 HHs surveyed)
In US as a whole
 (1
in 6 HHs surveyed)
Census 2000 Survey Topics for
Persons







Ancestry
Migration
Physical Disability
Income
Marital Status
Occupation
Journey to Work





Place of Birth
Education
Language
Veteran Status
Labor Force Status
Census 2000 Survey Topics for
Families
Grandparents as caregivers
 Poverty

Census 2000 Survey Topics for
Household Units








Vacancy Status
Units in Structure
Number of Rooms
Number of Bedrooms
Farm Residence
House Value
Monthly Rent
Housing Costs





Year Moved into
Residence
Plumbing and Kitchen
Facilities
Heating Fuel
Telephone Service
Vehicles Available
ACS Concepts,
Definitions, Overview
What is the ACS?




A large, continuous demographic survey
Produces annual and multi-year estimates of
characteristics of population and housing
Produces information for small areas including
tracts and block groups and is updated every
year
Key component of the reengineered 2010
Census of Population and Housing
ACS Background
Leslie Kish’s idea for a “rolling census”,
Roger Herriot’s suggestion for decadal
census program with continuous survey,
Chip Alexander and others efforts for
Continuous Measurement Survey
 Context of early 1990s: simplify decennial
census, reduce census costs, provide
more timely data

ACS Sample Design
Contact about 3 million households each
year, about 250,000 per month, in every
U.S. county
 Survey includes households in all 50
states, District of Columbia, and Puerto
Rico and will include both housing units
and group quarters

Sampling Rates
Occupied
Housing Units
per sampling
unit
=<200
Census 2000
Survey
ACS Over 5
Years
50.0%
50.0%
201-800
50.0%
~35.0%
800-1,200
25.0%
~17.5%
1,200-2,000
16.7%
~12.0%
2,000+
12.5%
~8.5%
Sample Design
Accumulate sample over time to produce
lowest levels of geographic detail
 Annual estimates for population size of
65,000+
 Three-year averages for 20,000+
 Five-year averages for census tracts and
block groups

ACS Implementation Schedule

ACS testing and development: 1996-2004

ACS full implementation: Jan 2005

First full implementation data products:
Summer, 2006
Data Availability Schedule
Type of
Data
Annual
Estimates
Annual
Estimates
3-year
averages
5-year
averages
Population Data for the Previous Year Released in the Summer of:
Size of
2003 2004 2005 2006 2007 2008 2009
Area
>=250,000
X
X
X
X
X
X
X
>=65,000
>=20,000
Census
Tracts and
Block
Groups
X
X
2010
X
X
X
X
X
X
X
X
Two Major Forms of ACS Data
1. Summary Files/Tabulations
2. Microdata samples of individual
household records (PUMS)
Summary Files/Tabulations
These are tables that report summary of
cases for different categories
--# persons by age and sex for a
census tract
--% of families with grandparent
caregiver in a county
 Not all possible combinations of variables
can be tabulated, so only ones of major
interest are tabulated

Advantages of Summary
Tabulations
The major advantage is that they present
a standardized tabulation for similar
geographic units
 For example, one can obtain the
proportion of Black households in poverty
of all census tracts in a metropolitan area

Limitation of Summary
Tabulations
Summary tabulations are presented in a
fixed format with limited flexibility for the
analysts to make adjustments
 Analysts can collapse categories but there
is not ability to obtain more detailed
categories or to add additional variables

U.S. Census Geography
Geographic Concepts
Census geography is important for
locating data but also because of the
organization of the geographic hierarchy
 Census geography is structured in a
generally hierarchical fashion, ranging
from larger to smaller units, with smaller
units contained within the boundaries of
larger units

Geographic Hierarchy










United States (n=1)
Region (n=4)
Division (n=9)
State, including D.C. (n=51)
County (or equivalent, n=3,141)
Place (n~39,000) (not in strict hierarchy)
Census tract
Block group
Block (n~7,000,000)
Housing unit
Supplemental Geographic Units
Urbanized area and urban/rural areas
 Metropolitan areas (MSA and CMSA)
 American Indian and Alaska Native areas
 Congressional districts
 ZIP code areas
 Traffic Analysis Zone (TAZ) areas
 School districts
 User-Defined Area Programs (UDAP)

Hierarchy of Data Availability
Corresponding to the hierarchy of
geographic units is a hierarchy of the
detail of census data
 More detail (more variables and more
categories in variables) are available for
larger geographic units
 Census tract data has more detailed data
than blocks or block groups

Data Access
The U.S. Census Bureau website offers
access online to ACS profiles and tables
http://www.census.gov/acs/www/
 Users can request special tabulations for
ACS data
 There are several Secure Census
Research Centers that may offer
specialized data access

Microdata (PUMS)
The second main ACS data type closely
resembles the actual data collected in the
ACS survey questionnaire
 All person identifiers are removed and the
microdata have limited geographic
identifiers

PUMS
PUMS data include original survey
variables and some derived measures
 Includes records for housing unit and for
each person in occupied housing units

Uses of PUMS
Microdata is a flexible form of survey data
 Offers more specialized combinations of
data that researchers can craft for special
purposes
 Downside is that geographic areas are
fairly large

ACS Sampling Frame
Select households from Master Address
File (MAF) updated from 2000 census
 Continuously update MAF through use of
(a) delivery sequence files from USPS and
(b) updated addresses through the U.S.
Census Bureau’s community address
updating system

ACS Data Collection Process
Obtain overlapping monthly samples using
three data collection systems
 Mail: make initial attempt at collection by
mail questionnaire
 Phone: telephone follow-up of incomplete
mail returns from 3 CATI facilities
 Personal visit: subsample incomplete
returns by CAPI using laptops

Data Collection Process: Response
Rates by Mode and Nativity
Percent of Interviews
80
70
60
50
Native
Foreign
40
30
20
10
0
Mail
Phone
in-Person
English Proficiency and Response
Rates, Houston
Speaks English Well
80
70
60
50
40
30
20
10
0
Native
Foreign
Mail
InPerson
Does Not Speak
English Well
80
70
60
50
40
30
20
10
0
Native
Foreign
Mail
InPerson
Comments about Foreign-Born





Current mail questionnaire in English only, with
Spanish upon request
Phone and in-person visit available in English
and Spanish
But: language barriers are problem
Currently, informal methods are used to
complete the interviews
Need improved methods for other languages
ACS Item Nonresponse, 2003






Lowest Rates for:
Sex
Citizenship
Phone availability
Grandchildren at
home
Monthly condo fee






Highest rates for:
Mobile home costs
Property insurance
Other mortgage
Real estate taxes
Year house built
Sample Weights
Initial weights reflect the probability of
selection
 Weights are adjusted for interviewed
households to account for noninterviews
 Weights are adjusted to independent
housing unit and population estimates (i.e.
population controls)

Population Control Totals



Intercensal population estimates are produced
by updating previous decennial census results
with administrative records
Control totals for housing units and population
(by age, sex, and race/ethnicity) are made
annually for counties (or group of counties)
Housing unit and population adjustment factors
are applied to sample weights to derive housing
and population weights consistent with
population control totals
Some Key Reminders
Annual data for small areas will be moving
five-year averages
 Annual data for all areas involve a “margin
of error” due to sampling

Differences from Traditional
Census
1. Data Content
 The ACS survey questionnaire includes
basically the same set of data content as
the survey questionnaire (the “long form”)
for the decennial census 2000

Differences from Traditional
Census Survey
2. Variable Definitions
 Many of traditional census survey
questions are asked in a slightly different
form
 Census and earlier ACS include a racial
category for “Black, African American, or
Negro”
 ACS for 2003 and after includes a
category for “Black or African American”

Differences from Traditional
Census



3. Temporal Aggregation
ACS: for larger (65,000+) population units, data
will be available annually, albeit collected
throughout the year
For smaller geographic units, data will be
aggregated over time, for moving 3-year and 5year averages
Differences from Traditional
Census



4. Residence Rules
ACS collected data using a current residence
rule, a “two-month rule” that defines a resident
who has been in the same place for at least two
months
Unlike the decennial census that uses usual
residence rule, collecting April 1st data on the
characteristics of usual residents
Differences from Traditional
Census
5. Reference Period
 The traditional census used April 1 as
reference for time related variables

 Age
 residence

5-years prior
Because of the rolling nature of the ACS,
the reference date is always shifting
Differences from Traditional
Census
6. The Migration Question
 The traditional census survey asked about
residence 5-years prior to the April 1
 ACS asked about residence 5-years prior
in 1996-1998
 ACS shifted to residence 1-year prior in
1999

Multi-Year Statistics
Most multi-year statistics are calculated by
combining the ACS data for each year
 Estimates are computed using the
geographic boundaries for the most recent
year of the period
 Dollar valued data items are adjusted for
inflation to the most recent year in the
period

Example of Multi-Year Statistics

Percent foreign-born for year 1:
Number Foreign-Born
------------------------------------------
Total Population
N1
=
-----
T1

Percent foreign-born for three-year
estimate:
N1 + N2 + N3
--------------------T1 + T2 + T3
Multi-Year Estimates for Median
Medians are produced using combined
data for all years
 Medians in ACS are not produced by
taking the average for medians for each
year
 A 3-year median household income is
calculated by combining the household
records for all 3 years, adjusted for
inflation, and determining the median from
the combined data

Issues with Multi-Year Statistics
Trend analysis for areas of different sizes
with different multi-year statistics: single
year for states and five-year statistics for
census tracts
 3 and 5-year statistics smooth changes
over time and will not reveal the greater
annual fluctuations

Example: Percent Foreign-Born
SingleYear
3-Year
3-Year
3-Year
2005
2006
2007
2008
2009
2010
20.0
21.2
23.3
28.6
32.6
35.1
21.5
24.8
28.6
3-Year
5-Year
5-Year
32.2
25.9
28.9
Interpreting Multi-Year Statistics
Because data users have not had actual
experience with multi-year statistics, there
is much to learn about practical issues of
interpretation
 With the availability of multi-year statistics,
it will be useful to accumulate case studies
that illustrate the best practices for their
uses and interpretation

Nonsampling Errors in ACS


Key ones to worry about include biases due to
nonobservation, due to noncoverage
(incomplete frame for migrant farmworkers, for
example) or nonresponse (failure to complete
interviews for non-English speakers, for
instance)
And biases due to observations: response
biases (interviewing, counting, or measuring)
and processing biases (coding, tabulating, and
computing)
Handling Nonsampling Errors
U.S. Census Bureau staff has long
experience with large national survey
 Annual report available entitled “Accuracy
of the Data”
 Protects against nonsampling errors by
extensive evaluation
 Release occasional papers reporting their
studies of nonsampling errors

Concerns about Nonsampling
Errors
Migrant and seasonal farmworkers: have
traditionally be a very difficult group to
cover in decennial census. Ongoing
nature of ACS should help
 Recent immigrants: often live in complex
households, may have concerns about
participating in survey, and often have
limited English-language proficiency

Sampling Error
ACS data estimates the actual figures that
would have been obtained by interviewing
the entire population
 Sampling error arises due to the use of
probability sampling
 With proper probability sampling, we can
make sample estimates with measures of
the deviation of the estimate due
(primarily) to sampling errors

Calculation of Standard Errors
ACS website provides additional
references on standard errors and their
calculation for ACS data
 For many users, it would be helpful to
include formulas in excel for routine use

Imputation: Substitution





U.S. Census Bureau edits collected data to
improve quality
Check for erroneous and missing data items
Substitution includes the imputation of an entire
record for a missing housing unit or person
Replacement record is usually drawn randomly
from a set of previously processed records
Sometimes called “hot-deck” imputation
Imputation: Allocation
Allocations are made to filling missing or
incorrect entries
 Allocation for missing items is most
common when a questionnaire item was
left blank
 Inconsistency occurs, for example, when a
respondent states that they moved to the
United States before they were born

Allocation Techniques
In some cases, logical imputation is used
to replace a missing item with a response
that is based on other items (for example,
assuming that a person born in Costa Rica
must be Hispanic)
 Other items are replaced by random
selection from a set of data for similar
persons

Reporting on Allocation



ACS website has extensive documentation on
the rate of allocation for geographic areas and
data items
PUMS data includes allocation flags for data
items that can be used for detailed analysis of
allocation
With PUMS data, analysis can be replicated for
items with non-allocated responses or my using
Rubin’s multiple imputation techniques