Dear John –
Here is my 2007 document about LEHD On the
Map.
http://www.fhwa.dot.gov/planning/census/lehdonthemap.htm
We have not had time to re-evaluate new
data (QCEW 2005 and 2006 ) released in the last couple of months
from On the Map.
It is VERY important to understand that
the LEHD On the Map includes “covered” employment only. This
means workers who are covered by unemployment insurance.
To answer John’s specific questions:
1. The workplace location is taken
from the QCEW (aka ES 202 files). The quality of the workplace location
relies on the quality of the QCEW files that EACH States provides to the CB,
particularly the quality and completeness of voluntary Multiple Site Businesses. For workers who work for a business with multiple sites, they are assigned to a
work location based on data from Minnesota
where the state requires that EACH employee be linked to a specific site, not just the employer. In other states, businesses are not required to link individual employees
to a specific site. For example, a large grocery business
with 10 stores in one county, may or may not report all 10 store locations, and
the assignment of an employee to one of the 10 stores uses
the results from Minnesota
to do the assignment. Some states expend more staff resources to
research businesses to build more
complete files of multiple sites, even when the business
itself does not report those locations.
2. Residence location is taken from
federal administrative records, and then moved slightly to protect
confidentiality. Most residences are kept within the same census tract. Fredrik Andersson presented a paper
at ASA in 2007 (?) on the proximity of the synthetic data to the real
data.
3. Social Security Number (SSN) is
the variable that ties the different datasets together, but the SSN is not kept
on the files. The actual SSN is changed into a unique ID. And the
data when reported in On the Map is not for a microdata record, but is grouped
as synthetic block data.
Here is the link to the Census Bureau’s documentation:
http://lehd.did.census.gov/led/library/tech_user_guides.html
The paper I relied on earlier was:
"LEHD Infrastructure Files and the Creation of the Quarterly Workforce Indicators" by J. Abowd; B.E. Stephens, L. Vilhuber, F. Andersson, K.L. McKinney, M. Roemer, and S. Woodcock, dated December 5, 2005
There is an NCHRP 08-36 project, task 81
which is a small (“Quick Response”) research project to examine how
ACS and LEHD On the Map could potentially be combined. Cambridge
Systematics is conducting the research, and the NCHRP contact is Nanda
Srinivasan.
I don’t know why the word
“synthetic” is raising so many red flags. Transportation
planners have long used FRATAR and
IPF, which results in synthetic data. Another example of synthetic data
is where TRANSIMS is using a
combination of Census 2000 block
data with Census 2000 PUMS to create
synthetic households for each
block.
I don’t think that synthetic data
can summarily be called GOOD nor BAD. Data users
need to understanding the process and the data sources used
in the synthesis process. Because
the sample size in ACS is MUCH smaller than the decennial census “long form” in 1990 or in 2000, we
(the CTPP group) are talking much more about data synthesis for the ACS data,
because the Census Bureau’s Disclosure Review Board has
established more stringent rules about what can or can’t be released from
the ACS for CTPP to protect individual confidentiality. http://trbcensus.com/drb/
Hope this helps.
Elaine Murakami
FHWA Office of Planning (Wash DC)
206-220-4460 (in Seattle)
From: ctpp-news-bounces@chrispy.net
[mailto:ctpp-news-bounces@chrispy.net] On
Behalf Of John Hodges-Copple
Sent: Monday, October 06, 2008
5:39 AM
To: ctpp-news@chrispy.net
Subject: [CTPP] seeking guidance on
worker flows from the local employmentdynamics On The Map data
Does anyone have a short, "plain English"
explanation of the residence-to-workplace flows from this data and how it
compares to the old long-form commuting data from the 2000 and earlier censuses (censi?). I read "synthesized"
data and little red flags go up. Specifically, is this data based on
actual residence and workplace data of real individuals (as with the Census), or are the residence and workplace locations
from different data sources and the travel between the 2 synthesized in
some way, as a travel demand model would create travel patterns between
the 2?
Any guidance would be appreciated; my brief hunting through
the documentation didn't give me the clear specifics I was hoping.
John Hodges-Copple, Planning Director
Triangle J Council of Governments
PO Box 12276
Research Triangle Park, NC 27709
919-558-9320
johnhc@tjcog.org
www.tjcog.org
----- Original Message -----
Sent: Thursday, October
02, 2008 11:36 AM
Subject: RE: [CTPP] Need
your thoughts on CTPP products using
ACS standardtables
Elaine,
The
tables currently found in the ACS have been sufficient for my needs and
concerns. The idea expressed by Nathan is intriguing (if I understand it
correctly); by “multiple geographic units”, do we mean various MCDs, TAZs or the 20,000 population areas?
Concerning
the “Journey to Work Trends”, I made use
of that data primarily as comparative analysis for the Twin Cities region to other
MSAs and as a template for a more detailed look at Minneapolis-St.Paul.
However, given the workload that appears to exists, I don’t believe that
updating the report to include the 2005-07 information would be useful enough to spend additional time and resources
….at least for my specific needs and wants.
BOB
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size=2 width="100%" align=center tabIndex=-1>
From: ctpp-news-bounces@chrispy.net
[mailto:ctpp-news-bounces@chrispy.net] On Behalf Of Murakami,
Elaine
Sent:
Wednesday, October 01, 2008 4:18 PM
To:
ctpp-news@chrispy.net
Subject:
[CTPP] Need your thoughts on CTPP products using
ACS standard tables
Hi Everyone –
I
bet you have a lot of questions about CTPP using the first 3 years of
ACS and TAZs, but unfortunately, I
can’t answer them yet!
Given the
current uncertainty of the next CTPP (“custom
tabulation”) using the ACS, we
are moving forward to develop products using
standard ACS products. Some of you will recall that we created a series using the first 2005 ACS data products. They
are posted on both the FHWA web http://www.fhwa.dot.gov/planning/census/2005tpoverview.htm
and on the AASHTO web
http://ctpp.transportation.org/
On December
9, 2008, the Census Bureau plans to
release the first 3-year ACS products (surveys completed in 2005, 2006 and
2007). The minimum population threshold is 20,000 for the 3-year
products, compared to 65,000 population for the ACS 1-year products. So,
while the data is still “swiss cheese,” that is, geographic
coverage has holes, a lot more geographic units will be available.
The results are still subject to the Census
Bureau rules of “collapsing and filtering” which means that
sometimes the data have been suppressed and you will see an
"N".
We
are now designing new profile sheets, in which we plan to include data from
2000 (using Census Summary File 3 and CTPP2000) and from 2005-2007
ACS. Please let me know if you have any recommendations for
specific tables to include (the data must
be available in both 2000 and from the 2005-2007 ACS). One
recommendation from Nathan Erlbaum (NYS DOT) is to create a spreadsheet
macro that will sum up multiple geographic units and re-calculate the Margin of
Error (using the materials on Page
96-98 in NCHRP Report 588).
Also,
I am wondering if there is any interest in an updated “Journey to Work
Trends” report to include the 2005-2007 ACS results. http://www.fhwa.dot.gov/ctpp/jtw/index.htm
This report was limited to metropolitan areas with population over 1 million,
but had trend data including 1960, 1980, 1990 and 2000. Because of redefinitions of metropolitan areas by
OMB, the data need to be accumulated from county records for historical
comparability, which makes for quite a bit of work. The last report
used the 1999 definition, but the
2005-2007 ACS data will be reported using
the 2007 OMB definitions (I think). My question for you is: is this
report useful enough to spend time
and resources on?
Thanks
in advance for your opinions.
Elaine
Murakami
FHWA Office of Planning (Wash
DC)
206-220-4460 (in Seattle)
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