Prepared for the 2010 SDC-CIC Joint Steering Committee Meetings February 23, 2010

1. 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—2009 3-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 mark.e.asiala@census.gov