Robert:
Well, the ACS data is what it is – can’t get around
that. The sample size is smaller than that used for the 2000 Decennial
Census sample survey (the equivalent of about 12% versus about 16%), so there
are indeed many who are dissatisfied with the resulting higher margin of
error. This dissatisfaction is probably increased because Census did not report
the margin of error until the ACS came along, in the past allowing Census users
(myself included) some degree of blissful ignorance of the actual level of
uncertainty. At the small area level, notable error rates actually have
been in the sample data all along. Whether it will “not be good”
at the block group level will depend on how good it has to be for your
purposes, and on what data element you are measuring (e.g., smaller percent margin
of error for SOV rates than for bicycle commuters).
Block groups are of comparable size nationwide, for small
communities and large, ranging in the 2000 Census from about 600 to about 3000
and averaging about 1200 (the 2000 Census geography will be that used in the
2005-09 ACS product). The ACS block group data consequently will be of
comparable utility for small communities and large, since it is the size of the
block group that counts, not the size of the community. One exception to
this rule: Census uses higher sampling rates in low population areas (e.g.,
small towns and small rural counties) so that they can get a large enough
sample to achieve statistical significance when they have to report data for small
political jurisdictions.
Bottom line: for better or worse, ACS 2005-09 block group data
is all we will have in the next few months with small area socio-economic and journey-to-work
characteristics, unless one has the resources to do one’s own surveys.
As Ed Christopher pointed out, the 2010 block data also will be available for
our use in delineating new TAZs, though it will be limited to basic demographic
information, dwelling counts, and owner vs. renter vs. group quarters.
Pete Swensson, Senior Planner
Thurston Regional Planning Council
2424 Heritage Ct. SW
Olympia, WA 98502
(360) 741-2530 (direct line)
(360) 956-7575 (main desk)
(360) 956-7815 (fax)
This e-mail and any attachments are for the use of the addressed
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From:
ctpp-news-bounces@chrispy.net [mailto:ctpp-news-bounces@chrispy.net] On
Behalf Of Allen, Robert
Sent: Monday, October 11, 2010 7:19 AM
To: 'ctpp-news@chrispy.net'
Subject: RE: [CTPP] RE: TAZ delineation for CTPP (2006-2010)
tabulationSCHEDULE
Pete,
The information that I have been receiving through the Texas
Transportation Institute has been that the 2005-2009 ACS data will not be good
at the block group level, at least not for places like Abilene, TX (pop. appx.
120,000). If you have been getting different information, I would very
much like to know, as it is very important due to the timetable for our current
travel demand model update.
Robert R. Allen, AICP
Abilene MPO Transportation Planning Director
400 Oak Street, Suite 102, Abilene, TX 79602
Office (325) 676-6243
Fax (325) 676-6398
Cell (325) 513-4615
From: ctpp-news-bounces@chrispy.net
[mailto:ctpp-news-bounces@chrispy.net] On Behalf Of Pete Swensson
Sent: Friday, October 08, 2010 3:36 PM
To: ctpp-news@chrispy.net
Subject: RE: [CTPP] RE: TAZ delineation for CTPP (2006-2010) tabulation
SCHEDULE
I’ll just jump in. I am on the CTPP Oversight
Committee that prepared the “Business Rules” for delineating the
TAZs for which Census will report the data.
Census has been collecting journey to work data through the
American Community Survey nationwide since 2006 that will go into the CTPP
2006-2010 tabulation. They need all of us FIRST to delineate our TAZs for
them to create the tabulation. So you won’t be able to wait to see
the data first in order to determine how best to delineate your TAZs.
Sometime around December of this year, the 2005-2009 5-year
dataset will come out, providing data down to the block group level (2000
census block group geography), and you may find that useful in determining how
you want to delineate your TAZs. It won’t be exactly what you are
looking for geographically, the standard tables will not be as specifically
tailored to transportation modelers, and the data won’t be benchmarked to
this year’s decennial census like the 2006-2010 dataset will. But
it may give you some useful data.
Pete Swensson, Senior Planner
Thurston Regional Planning Council
2424 Heritage Ct. SW
Olympia, WA 98502
(360) 741-2530 (direct line)
(360) 956-7575 (main desk)
(360) 956-7815 (fax)
This e-mail and any attachments are for the use of the addressed
individual. If you have received this e-mail in error, please notify our
systems manager. TRPC has taken responsible precautions to ensure no
viruses are present in this e-mail, however we do not accept responsibility for
loss or damage arising from the use of this e-mail or attachments.
From: ctpp-news-bounces@chrispy.net
[mailto:ctpp-news-bounces@chrispy.net] On Behalf Of Curt Hutchings
Sent: Friday, October 08, 2010 12:20 PM
To: ctpp-news@chrispy.net
Subject: [CTPP] RE: TAZ delineation for CTPP (2006-2010) tabulation
SCHEDULE
Elaine,
Please excuse my
ignorance. I have had questions about how the Census Dept. would collect
TAZ data for the Census. I have been waiting for information like you
have provided below. Can you give me any additional information? We
are in the process of modifying our TAZ structure now and want, If possible to
use the new information in this count. Any thoughts?
Thanks,
From:
ctpp-news-bounces@chrispy.net [mailto:ctpp-news-bounces@chrispy.net] On
Behalf Of Elaine.Murakami@dot.gov
Sent: Wednesday, October 06, 2010 10:32 AM
To: ctpp-news@chrispy.net
Subject: [CTPP] TAZ delineation for CTPP (2006-2010) tabulation SCHEDULE
At our monthly CTPP Technical meeting last week, April
Avnayim of the Census Bureau Geography Division, gave us an update on the TAZ
delineation software schedule.
November 2010: agencies verify contact names by
reviewing file at Cambridge Systematics ftp site, and report any changes to
Liang Long.
December 2010: final delivery of software by Caliper
to CB
February 2011: web-based training coordinated with
FHWA
January thru March 2011: delivery of software and
Census 2010 data and geographic files on a rolling basis.
Each state will get 3 – 4 months to delineate their
TAZ and TADs and return the files to the Census Bureau.
July 2011: all files MUST be returned to CB Geography
Division.
Please note: TAZs for CTPP tabulation do not
necessarily match the TAZs for your travel demand model. Because the ACS
sample is small, some agencies are planning to make the TAZs for CTPP LARGER
than their model TAZs, e.g. combining their model TAZs together. Also, TAZs for
CTPP are census block equivalencies. You will NOT be able to modify the
TIGER segments (which was possible in the CTPP2000). Finally,
agencies are NOT required to define TAZs or TADs. If you do not define
TAZs, then census tracts will be used as the default geography for CTPP
(2006-2010) tabulation. However, even if you do not define TAZs, we
recommend that you create TADs (population threshold of 20,000) by combining
census tracts together.
The TAZ business rules are posted on the FHWA webpage: http://www.fhwa.dot.gov/ctpp/tazddbrules.htm