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					Brave New World
Using the
                        Why?

ACS will provide

  •   Better quality data
  •   More frequently (every year)
  •   Better knowledge of local areas
  •   Cost savings ($1 billion)
Goal is not to produce a
population count but rather to
produce the characteristics of
the population.
        Effect on
        Decennial Census



No more long form —
   In 2010, only 100% data
                          Better Quality Data
                           Over Decennial
                               Because

•   Field representatives in every county will
    have local knowledge
    More highly trained, greater longevity, more highly paid
          How to reach hard to enumerate populations
          If a language barrier exists
          How to handle local situations


•   More extensive followup
    Computer-assisted telephone interviews
      as well as in-person visits
                               However…

Smaller sample size – 12.5% instead of 17%
   — 12.5%   after 5 years; initially is about 2.5% per
    year
      — Oversampling  in smallest governmental units so “about
       2.5%” actually ranges from 1.7% to 10%

   — Bureau projects that “the estimates of sampling
    error for the five-year ACS estimates…will be
    about one-third higher than…decennial census
    estimates. We believe this is acceptable given
    the reductions of nonsampling error…”
                                  How can they do
                                   it every year?

Rolling sample on a five-year cycle
                                    Huh?
(Years reflect data collection)
Release Schedule
                Data Available
                    Now!


• All States
• Puerto Rico
• Most areas of 65,000 or more
                     What’s Different?

• Data for smaller communities (<65k) in 3-
  and 5-year averages
  –   Use larger communities’ 3- and 5-year averages to
      compare with smaller communities

• Margin of error more transparent
  –   All estimates presented with lower and upper
      bounds of 90% confidence interval
  –   Can be very large compared to the estimate
Median Value of
Owner Occupied Units by Year Built
            Statistics Break!

            32
       23   25
                                23
       25   24
                                25
            23
       23                       23
            23
Mode                            24
       24   23
                                18
            18
       18                       32
                                23
       32
       23
               Implications with
                  Multi-year
                Averaged Data


            Green Handouts

Estimates lag behind the actual trend
  • Handicap in beginning, especially
  • Fluctuating figures hard to track – will
    read as flat line
                       Implications with
                          Multi-year
                        Averaged Data

• What geographic boundary applies?
   – most recent within the average (will result in more TIGER
     updates)

• Which year’s dollar value applies?
   – most recent within the average (others inflation-adjusted)

• With no single Census date, what does “residence”
  mean?
   – ―current‖ instead of ―usual‖ (2 months rule)
   – seasonal populations may appear in any category of "second
     residence" (3 questions in 2005 questionnaire)
Data Collection / Reference Period




                     Griffin & Waite, 2006, p. 212
           Summary -
         Comparisons with
          Decennial Data


    Yellow Handout
At-a-glance Comparison

  See also, Blue Handouts
 Variable-Level Comparison
  Understanding the
Numbers – Use the MOEs
Comparing Two Estimates

•   If have two estimates, need to determine if the
    apparent differences are ―real‖

•   Quick and dirty method is to ―eye ball‖ whether
    the confidence intervals overlap
Interpreting Estimates
Comparing Two Estimates
(the easy way)

•   If the confidence intervals of two estimates do
    not overlap, then the two estimates are
    statistically different

•   If the confidence intervals of two estimates do
    overlap, then the two estimates are not
    statistically different (maybe)
    Sampling Error & Standard Error

•   Sampling error occurs when estimates are
    derived from a sample rather than a census
    (complete count) of the population.

•   Standard error is an estimate of sampling
    error – how precise the survey estimates are
Sampling Error & Margin of Error


 •   Margin of Error = standard error for a given
     confidence interval (typically 90 percent). A measure
     of the precision of the estimate at a given confidence
     interval

 •   Sampling error is often reported as the estimate ―plus
     or minus‖ the margin of error
Margin of Error (MOE)



•   MOE = 1.65 * Standard error
       1.65 is used for the 90 percent confidence interval


•   Standard Error = MOE/1.65
Comparing Two Estimates

•   Need to do a formal test of statistical
    significance if the confidence intervals do
    overlap
                 (The Hard Way)
Statistical Testing - Steps


1.   Calculate the difference in the estimates

2.   Calculate the standard errors of each
     estimate
Statistical Testing - Steps

3.   Calculate the standard error of the difference

4.   Calculate the MOE of the difference

5.   Compare the difference between the
     estimates to the margin of error of the
     difference.
Statistical Testing - Steps

 6.   If the difference in the estimates is greater
        than the margin of error of the difference,
        then you conclude that the two estimates
        are statistically different

 7.    If the difference in the estimates is less than
       the margin of error of the difference, you
       conclude that the two estimates are not
       statistically different.
Go to Spreadsheet

(The easy way to do the hard way)
                     Two Tools
http://www.mdp.state.md.us/msdc/SDC_meeting_
040407/SDCmeeting040407.htm
(little simpler)


http://www.sdcbidc.iupui.edu/sharing/tools.html
(little more flexible)
Summary

•   2005 ACS is HH pop and not total pop
•   Use CB estimates, NOT ACS for A/S/R/ state &
    county estimates
•   Need to evaluate apparent differences to see if
    statistically significant
•   A good idea to look at MOE to evaluate how good an
    estimate is

•   May need to wait for 3 or 5-year estimates to get data
    with acceptable margins of error
                   Funding Issues

• Fight every year but especially for ramp up
  (advocacy always welcome)
  – In same funding bill as Homeland Security
  – In FY2007, held to FY2006 budget

• Affects planning and implementation
  – handheld data collection devices
  – Group Quarters behind schedule
                         For More Information


               American Community Survey Web site
                 Advanced methodology section especially

                     (www.census.gov/acs/www)


American Community Survey Web site
                                                  State Data Center network for
Using the Data and Advanced Methodology                     local areas
              sections especially
                                                 (http://www.census.gov/sdc/www/)
      (www.census.gov/acs/www)


                       Subscribe to the ACS Alert at:

               http://lists.census.gov/mailman/listinfo/acs-alert
New Variables in ACS (2005)

•   Whether the household received food stamps
    in the previous 12 months and their value

•   The length of time and main reason for staying
    at the address (for example, permanent home,
    vacation home, to attend school or college),
    and

•   For women ages 15-50, whether they gave
    birth to any children in the past 12 months.
Possible Changes (2008)

New Variables
• Marital history
• Health insurance coverage
• Veteran’s service-related disability


Deleted Variables
• The length of time and main reason for staying
  at the address
Possible Changes

Other Changes (2008)
• To stay consistent with 2010 census
• To improve response on some items


Testing New Item – 2007
• Field of Bachelor’s degree
  Might be added in 2009
Table Number Trivia
B = basic or base tables
    provide the most detailed estimates on all topics
    and for all geographies.
C = collapsed version of a B table
     very similar to a B table with the same number
    (e.g., C07001 and B07001), but two or more lines
    from the B table have been collapsed to a single
    line in the C table. For example, the lines "75 to 79
    years", "80 to 84 years" and "85 years and over"
    from a B table may be collapsed to a single line of
    "75 years and over" in a C table.
* Not every B table has a collapsed version.
Table Number Trivia

The next two characters identify the primary subject of
the table.
                   01 = Age and Sex
                   02 = Race
                   03 = Hispanic or Latino Origin
                   04 = Ancestry
                   Etc.

   The next three digits are a sequential number,
   such as 001 or 002, to uniquely identify the table
   within a given subject.
Table Number Trivia

For select tables, an alphabetic suffix follows to indicate that a
table is repeated for the nine major race and Hispanic or Latino
groups:
        A = White Alone
        B = Black or African American Alone
        C = American Indian and Alaska Native Alone
        D = Asian Alone
        E = Native Hawaiian and Other Pacific Islander Alone
        F = Some Other Race Alone
        G = Two or More Races
        H = White Alone, Not Hispanic or Latino
        I = Hispanic or Latino
Table Number Trivia

For select tables

•   Final alphabetic suffix "PR" = a table used for
    Puerto Rico geographies only

•   For some geography-based subjects, the
    wording of the Puerto Rico Community Survey
    questionnaire differs slightly but significantly
    from the ACS questionnaire.

				
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