1. Census Background Census: 100 Percent Count of Units
Survey: Sample of Units

2. Censuses Decennial Census: Population and Housing
Economic Census: Business and Industry
Agriculture Census: Farms
Census of Government: Local and State

3. 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

4. International Program Center
Part of U.S. Census Bureau Population Division
Assist in Census data collection and processing for countries throughout the world

5. 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

6. 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)

7. 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

8. Census 2000 Survey Topics for Families
Grandparents as caregivers
Poverty

9. 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

10. ACS Concepts, Definitions, Overview

11. 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

12. 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

13. 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

14. Occupied Housing Units per sampling unit
Sampling Rates
Occupied Housing Units per sampling unit
Census 2000
Survey
ACS Over 5 Years
=<200
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%

15. 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

16. ACS Implementation Schedule
ACS testing and development:
ACS full implementation: Jan 2005
First full implementation data products: Summer, 2006

17. Data Availability Schedule

18. Two Major Forms of ACS Data
1. Summary Files/Tabulations
2. Microdata samples of individual household records (PUMS)

19. 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

20. 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

21. 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

22. U.S. Census Geography

23. 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

24. 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

25. 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)

26. 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

27. Data Access
The U.S. Census Bureau website offers access online to ACS profiles and tables
Users can request special tabulations for ACS data
There are several Secure Census Research Centers that may offer specialized data access

28. 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

29. PUMS
PUMS data include original survey variables and some derived measures
Includes records for housing unit and for each person in occupied housing units

30. 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

31. 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

32. 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

33. Data Collection Process: Response Rates by Mode and Nativity

34. English Proficiency and Response Rates, Houston

35. 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

36. 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

37. 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)

38. 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

39. 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

40. 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

41. 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”

42. 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

43. 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

44. 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

45. 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
ACS shifted to residence 1-year prior in 1999

49. 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

50. Example of Multi-Year Statistics
Percent foreign-born for year 1:
Number Foreign-Born N1 =
Total Population T1

51. Percent foreign-born for three-year estimate:
N1 + N2 + N3
T T T3

52. 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

53. 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

54. Example: Percent Foreign-Born
2005
2006
2007
2008
2009
2010
Single-Year
20.0
21.2
23.3
28.6
32.6
35.1
3-Year
21.5
24.8
32.2
5-Year
25.9
28.9

55. 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

56. 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)

57. 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

58. 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

59. 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

60. 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

61. 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

62. 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

63. 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

64. 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