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					American
Community
Survey
(ACS)

  Oregon State Data Center Meeting
      Portland State University
           April 14, 2009
                                     1
Agenda
• ACS & the Decennial Census
  • Census 2000
  • 2010 Census
  • Key Differences in the ACS
• ACS Data Releases
• ACS Survey Methodology
• ACS Multiyear Estimates
• ACS Data Products
• Accessing ACS Data Online
                                 2
Census 2000




              3
ACS and the Decennial Census
Census 2000
In 2000, the Census used two questionnaires
   1. Short form (“counts”)

     Asked basic demographic and housing information, such as
     age, sex, race, how many people lived in the housing unit, and
     if the housing unit was owned or rented by the resident

   2. Long form (“characteristics”)

    Collected the same information as the short form but also
    collected more in-depth information such as income, education,
    and language spoken at home

     Only a portion of the population - - called a sample - - received
     the long form (average of 1 in 6 nationwide)
                                                                         4
2010 Census




              5
ACS and the Decennial Census
2010 Census

• 2010 Census to focus on the “counts” (100%)
  data
   – All addresses receive the same Census (short) form

• ACS will collect the “characteristics” (sample)
  data
   – 3,000,000 addresses in 2010 will receive the ACS
     survey in addition to the 2010 Census form

   – Short form questions are also asked on the ACS

                                                          6
        Key Differences
between the ACS and Census 2000




                                  7
ACS and the Decennial Census
Key Differences

• Residency
  – ACS uses “two-month” rule

  – Decennial census based on concept of “usual
    residence”

• Employment
  – Both ACS and Decennial ask respondents if they
    worked for pay “last week”

  – ACS collects data year-round and produces an
    average of the data collected for the period
                                                     8
ACS and the Decennial Census
Key Differences (continued)

• Income
   – Decennial census income data refer to the
     previous calendar year
   – ACS asks for income for the previous 12 months
• School enrollment
   – Decennial census asks if a person attended
     school “any time since February 1”
   – ACS asks if a person attended school during the
     “last 3 months”
Data Releases




                10
American Community Survey
Data Releases


• Goal is to produce estimates comparable to
  the Census 2000 long form data
  – Estimates cover the same small areas (down to
    the block group level) as Census 2000 long
    form, but with smaller sample sizes

• Caveat: Smaller sample size = Reductions
  in reliability of estimates


                                                    11
American Community Survey
Data Releases

• ACS estimates are period estimates
   – Describe the average characteristics over a
     specified period
   – Contrast with point-in-time estimates that describe
     the characteristics of an area on a specific date
• ACS releases 1-year, 3-year, and 5-year
  estimates for geographic areas that meet
  specific population thresholds



                                                           12
American Community Survey
Data Releases: Schedule




                            13
Census Geographic Entities:
        Hierarchy




                              14
15
Survey Methodology




                     16
American Community Survey
Methodology

• Sample includes about 250,000 addresses
  per month, or 3 million addresses each year,
• Group quarters populations included in the
  ACS since 2006
• Data collected continuously throughout the
  year by three modes
  – Mail
  – Phone
  – Personal visit
                                                 17
Caveats

• ACS data are estimates

• ACS data are not counts of the population or
  housing

• Population counts are produced from the
  decennial census
  – Counts are updated throughout the decade
    through the Population Estimates Program


                                                 18
ACS Estimates: Period Estimates

• Period estimates describe the average
  characteristics over a specific time period

• Point-in-time estimates describe
  characteristics as of a specific date




                                                19
Sampling Error
• The uncertainty associated with an estimate
  that is based on data gathered from a sample
  of the population rather than the full
  population

• Margin of error (MOE) measures the precision
  of an estimate at a given level of confidence

• MOEs at the 90% confidence level for all
  published ACS estimates
                                                  20
ACS Multiyear Estimates




                          21
ACS Multiyear Estimates
Definition

• A period estimate that encompasses more
  than one calendar year

• Period for ACS multiyear estimates is either 3
  or 5 calendar years
  – First release for 3-year estimate is 2008 (for
    period 2005-2007)
  – First release for 5-year estimate is 2010 (for
    period 2005-2009)
                                                     22
Constructing Multiyear Estimates

• Data are pooled across 36 or 60 months

• Data are weighted to produce estimates

• Estimates are controlled for age, sex, race,
  and Hispanic origin

• Multiyear estimates are not an average of
  1-year estimates


                                                 23
When to Use Multiyear Estimates

• No one-year estimate is available

• Margins of error for 1-year estimates are
  larger than required

• Analyzing data for small population groups




                                               24
Currency vs. Reliability
              Currency                            Reliability

1-year estimates provide information   Larger sample sizes produce
based on the last year                 estimates that are more
                                       statistically reliable


3-year estimates provide information   3-year estimates are based on 3
based on the last year and the 2 years times as many sample cases as 1-
before that                            year estimates


5-year estimates provide information   5-year estimates are based on 5
based on the last year and the 4 years times as many sample cases as 1-
before that                            year estimates



                                                                          25
Reliability




 Note: Fictional data


                        26
How to Label Multiyear Estimates

• Multiyear estimates do not represent any one
  year nor the midpoint of a period

• ACS estimates based on data collected from
  2005-2007 should not be labeled “2006” or
  “2007” estimates

• Correct labeling for multiyear estimate: “The
  child poverty rate for the 2005-2007 period
  was X percent.”
                                                  27
Inflation Adjustment

• Dollar-valued data items are inflation adjusted
  to the most recent year for the period

• Income, rent, home value, and energy costs

• Adjusted using inflation factors based on the
  Consumer Price Index (CPI)

• Adjustment designed to put the data into
  dollars with equal purchasing power

                                                    28
Population Controls

• Estimates of housing units and people
  controlled to the population estimates derived
  from the Population Estimates Program
• Multiyear estimates controlled to the average
  of the individual year’s estimates for the period




                                                      29
Population Thresholds for ACS Estimates
Review



                     1-year      3-year      5-year
                   estimates   estimates   estimates

 65,000 + people      X           X           X
 20,000+ people                   X           X
 Less than
 20,000 people                                X




                                                       30
Geographic Boundaries
• Multiyear estimates are based on geographic
  boundaries as of January 1 of the last year in
  the multiyear period

• Boundary Annexation Survey collects
  boundary changes

• Boundaries of other statistical areas will be
  updated every decade in conjunction with the
  decennial census

                                                   31
Comparing Across Geographies

Only compare the same type of estimate
     • 1-year estimates to other 1-year estimates
     • 3-year estimates to other 3-year estimates
     • 5-year estimates to other 5-year estimates

Same time period




                                                    32
Counties in Kentucky, by Population Size
                                      Figure 3: Counties in Kentucky by Population Size, 2007

   Population, July 2007
  Population, July 2007
                                                                   Franklin
                     Less than 20,000 people
              0.00 to 20000.00



                                                                                          Fayette
                     20,000 to 64,999 people
              20000.00 to 65000.00




                     65,000 or more people
              65000.00 to 800000.00




 Fulton




 Source: U.S. Census Bureau,
 American Community Survey Handbook for General Audiences
                                                                                                    33
Comparing Data in 2010


                  2009   2007-2009   2005-2009



Fayette County     X        X           X



Franklin County             X           X



Fulton County                           X


                                                 34
Comparing Across Time Periods

• Same geographic area
  – Use caution if geographic boundaries have
    changed over time

  – Easier to compare non-overlapping periods

  – Make comparisons using the same length time
    period




                                                  35
Comparing ACS Data with Census 2000

• Differences exist between ACS and Census 2000
• Comparisons can be made for most population
  and housing subjects
• Crosswalk available
  – “Compare”
  – “Compare with Caution”
  – “Do Not Compare”
  http://www.census.gov/acs/www/UseData/compACS.htm

                                                      36
Choosing the Estimates


These estimates allow for ten comparisons:

  –   1999-2001 vs. 2000-2002   –   2000-2002 vs. 2002-2004
  –   1999-2001 vs. 2001-2003   –   2000-2002 vs. 2003-2005
  –   1999-2001 vs. 2002-2004   –   2001-2003 vs. 2002-2004
  –   1999-2001 vs. 2003-2005   –   2001-2003 vs. 2003-2005
  –   2000-2002 vs. 2001-2003   –   2002-2004 vs. 2003-2005




                                                              37
Determining Which Estimates to Use

  1999 to 2001


                 2000 to 2002


                            2001 to 2003


                                           2002 to 2004


                                                          2003 to 2005




 1999        2000          2001        2002          2003          2004   2005

                                                                                 38
Summary on Multiyear Estimates
• Multiyear estimates are period estimates and
  should be interpreted and labeled as such

• Data users should consider the tradeoffs of
  currency versus reliability

• Comparisons between estimates of different
  geographies should be based on ACS data
  from the same time periods

• It is easier to compare estimates from non-
  overlapping periods
                                                 39
ACS Data Products




                    40
American Community Survey
Data Products

• Profiles
   –   Data Profiles
   –   Narrative Profiles
   –   Comparison Profiles
   –   Selected Population Profiles
• Tables
   –   Detailed Tables
   –   Subject Tables
   –   Ranking Tables
   –   Geographic Comparison Tables
• Thematic Maps
• Public Use Microdata Sample (PUMS) Files   41
Data Profiles   Data Profile




                               42
Narrative Profiles




                     Narrative Profile




                                         43
Comparison Profiles
    Comparison Profile




                         44
            Selected
Selected
           Population
            Profiles




                        45
                           Selected
Selected Population Profiles
                     Population Profiles




                                           46
Detailed Tables
Examples

• Sex by Age by Race and Hispanic Origin
• Means of Transportation to Work by Travel
  Time to Work
• Median Number of Rooms in Housing Units
• School Enrollment by Level of School
• Poverty Status in the past 12 Months by Sex
  and Age

                                                47
            Table Name

  Table
  Number
                                   Universe


                         Data Source


Collapsed
Version

                                              Margin of Error




                                              Detailed
                                               Tables

                                                                48
Detailed Tables –
Collapsed Version




                    49
Detailed Table




                 50
                            Detailed
Detailed Tables for Quality Measures
                           Tables for
                             Quality
                            Measures




                                        51
Subject Table List
                     Subject Table List




                                          52
                 Subject Table
Subject Tables




                                 53
Ranking Table




                54
Ranking
 Table




          55
Geographic Comparison Table




               Geographic
               Comparison
                 Table




                              56
Thematic Map




               57
Public Use Microdata Sample (PUMS)
                                     58
PUMS
• PUMS = Public Use Microdata Sample
• Includes a sample of untabulated records for
  individuals and housing units
• Provides access to custom tables that are not
  available through pretabulated ACS products
• Requires users to download data and analyze
  with statistical software, or access through
  DataFerrett
• Data users must calculate standard errors

                                                  59
Accessing ACS Data Online




                            60
Census Bureau Home Page
  http://www.census.gov




                          61
American FactFinder (AFF) Main Page
    http://factfinder.census.gov




                               American FactFinder is
                               the data access tool for:
                               (1) Decennial Censuses,
                               (2) American Community
                                   Survey,
                               (3) Annual Population
                                   Estimates, and
                               (4) Economic Censuses
                                   and Surveys.

                                                           62
American FactFinder
Data Sets Main Page




                      63
American Community Survey Main Page
  http://www.census.gov/acs/www




                                      64
   Questions?

           Linda Clark
Information Services Specialist
Seattle Regional Census Center
        (425) 908-3062
    linda.clark@census.gov
                                  66

				
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