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 Surveyshttp://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

NameSex AgeRelationship to HouseholderHispanic OriginRace (can chose multiple categories)Owner/Renter

Census 2000 Survey (Long Form)

Includes all Q’s on Short Form Densely populated sampling areas

(1 in 8 HHs surveyed) Sampling areas less than 2,500 persons

(1 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

Census 2000

Survey

ACS Over 5 Years

=<200 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 ScheduleData for the Previous Year Released in the Summer of: Type of

Data Population Size of Area

2003 2004 2005 2006 2007 2008 2009 2010

Annual Estimates

>=250,000 X X X X X X X X

Annual Estimates

>=65,000 X X X X X

3-year averages

>=20,000 X X X

5-year averages

Census Tracts and Block Groups

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

0

10

20

30

40

50

60

70

80

Mail Phone in-Person

Perc

ent

of In

terv

iew

s

NativeForeign

English Proficiency and Response Rates, Houston

0

10

20

30

40

50

60

70

80

Mail In-Person

Speaks English Well

NativeForeign

01020304050607080

Mail In-Person

Does Not Speak English Well

NativeForeign

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 5-year 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 variablesAgeresidence 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 N1

------------------------------------------ = -----

Total Population 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-Born2005 2006 2007 2008 2009 2010

Single-Year

20.0 21.2 23.3 28.6 32.6 35.1

3-Year 21.5

3-Year 24.8

3-Year 28.6

3-Year 32.2

5-Year 25.9

5-Year 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