26 Jun
2009
26 Jun
'09
9:40 a.m.
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 248/354-6520
APB Associates/SEMCC FAX 248/354-6645
28300 Franklin Road Home 248/355-2428
Southfield, MI 48034 pbecker(a)umich.edu