1. American Community Survey:. Use Of Independent Subcounty
American Community Survey: Use Of Independent Subcounty Population And Housing Estimates As Controls
Prepared for the 2010
SDC-CIC Joint Steering Committee Meetings
February 23, 2010
Presented by: Mark Asiala
Department of Commerce
U.S. Census Bureau
Washington, DC 20233 1

2. Background
Two estimates of total population available for subcounty area
Specifically places, minor civil divisions
ACS and Population Estimates Program (PEP)
Typically do not agree
Disconcerting to data users
Credibility problem for the ACS
Census Bureau has been investigating solutions to this problem for several years

3. Current Research Three part research program
Document the degree of inconsistency and look for commonalities of the most egregious examples
Develop and test several ACS weighting methodologies designed to reduce the degree of inconsistency
Evaluate the demographic impact of proposed methodologies on other characteristics besides total population.

4. Results of the Research
ACS tends to underestimate large places relative to the PEP.
We were able to identify an alternative weighting methodology that is successful at reducing the inconsistencies.
We found that the impact on other demographic characteristics tends to be small or in line with expectations.

5. Implementation Plans
Based on our research, the Census Bureau is confident that
We can attain improved consistency in estimates of total population for subcounty areas.
We can implement this new methodology without unintended negative impacts on either the estimates or the variances.
We are also confident that we can operationalize this new methodology this year.

6. Implementation Plans
We will implement this new methodology for the data products scheduled to be released this year including:
2009 ACS 1-year estimates
2007—2009 ACS 3-year estimates
2005—2009 ACS 5-year estimates
There will be a gradual inclusion of the 2010 Census data in the controls---topic for tomorrow.

7. Note: Controls for Multiyear Estimates
The controls used for weighting the multiyear estimates are equal to the average of the population estimates over the period.
For example, in the 2007— year estimates:
Control is average of 2007, 2008, and 2009 population estimates.
This is true for county-level controls now and will also be true for subcounty-level controls.
The multiyear estimates will not be controlled to the PEP estimate for any single year in the period.

8. Things to Know and Remember
Goal of the new methodology is to reduce the inconsistencies.
Does not ensure exact agreement between ACS and PEP.
For five-year, a population threshold will be used to determine if we try to use subcounty controls (2,500 or 5,000)
Multiyear products will control to average of subcounty estimates over the period.
Implementation
Begin with 2009 ACS products released in 2010
Phase-in use of 2010-based controls over the next two years. (details in tomorrow’s talk, “Break in Series”).

9. Contact Information