The first thing to understand is that while the ACS county
estimates are controlled to the census population estimates, the
sub-county estimates are not. The numbers that appear for
cities are just what the weighted data show. For Detroit, they are always
too low. There is always a lag in terms of getting new housing
units into the sampling frame (the Master Address File, or MAF), while
there is loss when a sample address turns out to be demolished or vacant.
I don't know if that the 2010 ACS data are going to be weighted to the
census results. I don't think they've thought about that yet. If
they are, there won't be any problem updating from April to July. We do
not usually see redone intercensal estimates after the census, and I'm
sure that there won't be any adjustment of ACS results.
Bottom line: be very careful in using whole numbers from the ACS, and
when you do, always round them to '00s (hundreds) so that people will
understand that they are estimates and not counts. ACS is really best for
the data that are expressed in percentage terms.
Patty Becker
At 05:28 PM 6/25/2009, you wrote:
For ACS 2005-2007 population and
housing occupancy/vacancy estimates, are people finding discrepancies
between ACS and other data sources, particularly in sub-county
geographies? ACS estimates are controlled at the county level and,
like the ACS 1-year data, ACS 2005-2007 population estimates are showing
disagreement with other data sources. For example, the Oakland
3-year ACS estimate shows the population at 372,000, when CA Dept. of
Finance estimates are over 400,000. This runs counter to the
on-the-ground anecdotal experience - ACS shows a loss of 30,000 people
during a period that showed an increase of 10,000 housing units.
Will the decennial census correct this? My understanding is
that Census 2010 numbers will be used to control 2010 ACS characteristic
data. There will need to be some adjustment, however, given that
the decennial census benchmarks population at April 1, and ACS uses a
July 1 population number. It's also my understanding that
population estimates for 2001-2009 will be updated, though retroactive
adjustments for ACS characteristics will not be done. Does anyone
else know something different about this?
Other thoughts about this?
Thanks,
Shimon
---------------------------------------------------------------
Shimon Israel
Associate Transportation Planner/Analyst
Metropolitan Transportation Commission
101 Eighth Street
Oakland, CA 94607-4700
(510) 817-5839 (office)
(510) 817-5848 (fax)
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Patricia C. (Patty) Becker
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