I'm cross-posting this message to our local, state, and national census listservs. I've updated our analysis of the 40 California Counties and 119 California Places with (household) population greater than 65,000. An excel workbook is on our web site, at: ftp://ftp.abag.ca.gov/pub/mtc/planning/ACS/ filename: California_ACS_compared2_CalifDOF.xls Table 1. Comparing Bay Area County Household Population: ACS2005 to DOF2005/06 (DOF = California State Department of Finance, our State Data Center) Table 2. Comparing Bay Area City Household Population: ACS2005 to DOF2005/06 Table 3. Comparing California County Household Population: ACS2005 to DOF2005/06 Table 4. Comparing California City Household Population: ACS2005 to DOF2005/06 Table 5. Compare Households, Household Population and Average Household Population (new, 8/18) One of our principal concerns is that there is a significant difference in household population - - comparing the ACS2005 data to our independent (Calif State DOF) estimates of household population - - in 13 of the 119 California Cities covered in the ACS2005 data, released this past Tuesday, 8/15. Six of the largest ten California cities are on this list: Los Angeles, San Diego, San Jose, San Francisco, Oakland, and Santa Ana. (Three of these: SF, SJ and Oakland, are in my region....) So, why the difference? 1. The ACS2005 is controlled at the county-level to the FSCPE population estimates. (FSCPE = Federal-State Cooperative Program for Population Estimates). These FSCPE county-level files are available here: http://www.census.gov/popest/datasets.html More on the FSCPE program here: http://www.census.gov/population/www/coop/fscpe.html Note that these FSCPE estimates include county- and state-level values for total population, household population and group quarters population. Also note that the FSCPE does not include estimates of either occupied dwelling units (households) or total units (occupied + vacant). 2. Our California State Department of Finance current population estimates (their "E-5" report series) is available here: http://www.dof.ca.gov/HTML/DEMOGRAP/ReportsPapers/Estimates/E5/E5-06/E-5tex… The California State DOF forecasting methodology is described in the above URL, and discusses the "housing unit method" used by DOF in some detail. (Makes good sense to me!) 3. Population estimates produced by the States may be different than population estimates produced by the Census Bureau. An excellent, insightful and educational article on current population estimates is included in the July-August 2006 edition of the APDU (Association of Public Data Users) newsletter, available here: http://www.apdu.org/. This article discusses a one-day conference on 7/19/06 co-hosted by COPAFS (Council of Professional Associations on Federal Statistics) and Sabre Systems. This is a must read for anyone interested in understanding possible issues in the control totals used in weighting/expanding ACS data. 4. What to do next? My recommendation is to be patient, and wait for the "total housing unit" data from ACS2005, expected for release this October 3rd. This will be the best information that city and county planners will have, when comparing ACS estimates of housing units to any independent estimates of housing units. The Table 5 in my XLS workbook is very revealing: the ACS is extremely valuable in indicating significant changes in average household size: San Jose's average household size is declining from 3.20 to 3.08; San Francisco from 2.31 to 2.23; and Oakland from 2.60 to 2.56. These are plausible trends, and trends we would not have predicted without the ACS. On the other hand, it appears that the ACS may be showing a 2.2 percent LOSS in the San Francisco City housing stock (actually, households derived by: household population divided by average household size, as published in American Factfinder); and a 3.1 percent LOSS in the Oakland City housing stock, 2000 to 2005. (To put this loss of 4,700 housing units in Oakland in perspective, this 4,700 housing unit loss is 1.6 times as high as the 2,900 housing units we lost in the 1991 Oakland Firestorm....) The fact of the matter is that housing units are a fairly durable good, and they don't disappear that easily. So, my conclusion is that improvements are needed in the FSCPE population estimates to incorporate changes in housing stock. Easier said than done, so it may be a few years before our housing numbers recover.... Hope this is helpful to the SDC networks and others, Chuck Purvis, Metropolitan Transportation Commission, Oakland, California (Affiliate Data Center in the San Francisco Bay Area) ************************************************************** Charles L. Purvis, AICP Principal Transportation Planner/Analyst Metropolitan Transportation Commission 101 Eighth Street Oakland, CA 94607-4700 (510) 817-5755 (office) [new, 8/1/05] (510) 817-7848 (fax) [new, 8/1/05] www: http://www.mtc.ca.gov/ Census WWW: http://www.bayareacensus.ca.gov/ **************************************************************