Robert:
The income data is tricky in another way: in the past Decennial
Census sample data, the question was asked of survey respondents around the
time of Census day, April 1. They were asked, what was their income for
the previous calendar year? Most people would have just done their income
taxes, and would have a pretty reliable idea of their income for that period.
Now ACS surveys the population every month of the year, asking what was their
income for the prior 12 months, which now most often splits calendar years.
Comparisons in 2000 of the Decennial Census Sample Survey versus the ACS method
have shown that this new method results in a lower estimate of income than the
methodology in the old survey, and I suspect it is because people now are
mostly guessing at their income rather than having a precise calculation at
hand.
Thus income is longitudinally comparable using ACS from one year
to the next, but it is not longitudinally comparable using ACS versus 2000
Census. You can expect it to be reasonably comparable horizontally from
one neighborhood to another for the same time period. On the other hand,
the Great Recession may have affected some neighborhoods more than others, and
this may not be captured very well by the long time period represented by the
ACS 5-year 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 Allen, Robert
Sent: Monday, October 11, 2010 11:57 AM
To: 'ctpp-news@chrispy.net'
Subject: RE: [CTPP] RE: TAZ delineation for CTPP (2006-2010)
tabulationSCHEDULE
Pete,
Thanks for your reply. I am looking primarily for household
incomes as the most urgent data. Income data has always been a
notoriously subjective item with wildly varying degrees of reporting accuracy,
both intentional and unintentional. I obviously need to do more direct
research with the Bureau about the ACS usefulness at various population
thresholds.
Robert
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: Monday, October 11, 2010 1:19 PM
To: ctpp-news@chrispy.net
Subject: RE: [CTPP] RE: TAZ delineation for CTPP (2006-2010) tabulation
SCHEDULE
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
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.