21 Sep
2010
21 Sep
'10
2:55 p.m.
Page 12 of this Census Bureau Compass Report gives some general
information on collapsing for statistical reasons.
http://www.census.gov/acs/www/Downloads/handbooks/ACSBusinessHandbook.pdf
However, little is out there on how the process actually works.
Starting on slide 3 of this 2006-7 power point are some details on the
mechanics of the process. If you look at these slides ignore slide 2 as
the disclosure rules have changed slightly.
http://download.ctpp.transportation.org/training/ACS%20data%20issues.ppt
Finally If you go to NCHRP Report 588 it says this about what I call
statistical collapsing...
"Table Variable Collapsing: As for the 2000 CTPP, the Census Bureau
expects to apply quality control measures on ACS data products for
geographic areas for which categorized tables could be misinterpreted.
Any table whose median distribution of covariance for individual cell
values is greater than 61 percent will be modified or suppressed for
that geography. For example, for a given geography for County X, for a
table with 18 means of transportation, individual covariances are
calculated for estimates of workers who drove alone, carpooled, etc. If
the median of these covariances isgreater than 61 percent, then these
modes would be collapsed to fewer categories according to predefined
collapsed table definitions. If the median of covariances for the
collapsed table still exceeds 61 percent, the table will be suppressed
for County X."
http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_588.pdf
Michael Moan wrote:
That is too bad. I have a feeling there is going to be
a lot of that for Rhode Island geography.
Michael C. Moan, Principal Planner
Office of Statewide Planning
Division of Planning
Department of Administration
One Capitol Hill
Providence, RI 02908
4012221236
--
Ed Christopher
708-283-3534 (V)
708-574-8131 (cell)
FHWA RC-TST-PLN
4749 Lincoln Mall Drive, Suite 600
Matteson, IL 60443
>> Ed Christopher <edc(a)berwyned.com>
9/21/2010 2:17 PM >>>
Typically the reason when data is not available like
Bike broken out for
both data sets and the same geography is that the data was collapsed.
The CB uses a statistical test on the data quality for each mode and
if the mode does not pass it is collapsed with other modes. when
looking at ACS data on factfinder you will find tables starting with a B
or C. The C means its a collapsed table.
Nordbo, John - DOT wrote:
Hello, everyone -
I'm forwarding this question from a colleague.
For Means of Transportation to Work, the 2006-2008 ACS detailed tables by place break out
bicycles in a separate line. The same question was asked on the ACS from 2003 to 2005 but
there does not seem to be a similar table to download; the 2003-2005 data groups bicycles
with taxi cabs, etc.
Can anyone tell me if data for bicycles only is available for 2003-2005, and if so,
where/how?
Thanks!
John P. Nordbo
Urban and Regional Planner
Bureau of Planning and Economic Development
Wisconsin Department of Transportation
4802 Sheboygan Ave Rm 901
Madison, WI 53707-7913
ofc: 608.267.7751
fax: 608.267.0294
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