Penny:
I would chime in that my experience suggests all data and findings should be compared as the differences, whether due to methodology, underlying assumptions, or actual observed change can add great insight and "point the way" towards the answers desired.
Such comparisons often highlight differences and should help analysts start to comprehend the weaknesses and strengths of data upon which they're building assumptions. It doesn't make one set of data more "right" than another, just a different perspective. I always ask "what does the comparison tell me?" Does the comparison yield differences and similarities I expect? Are the findings consistent with other "common wisdom"? If no, why not?
For example, take a few very different data sources: the CTPP, ACS, NHTS, QCEW, IRS, D&B and InfoUSA. Each include very different ways of estimating employment. All are incomplete but paint part of the picture. Taken together, I can see patterns and weigh the relative strength of each one's methodology to meeting a specific need.
How are part-time jobs treated? How about sole proprietors? How about workers with more than one job? Workers that work one day/week or month? 1099 workers? Volunteers? Seasonal workers? Military? Are there things missing, discounted or even double-counted in one vs. the other? Understanding Standard Error terms is one thing, understanding utility and suitability is quite another.
Even trying to answer a simple question such as "how many jobs/workers are there at a given moment in time" doesn't have a simple answer or at least there isn't one dataset that will answer it depending on the definition of job/worker I'm looking for to meet a specific need.
One “comparison” I was looking at in the 2000 vs. 2009 3 year data is a simple “relative order” of destination county in one dataset vs. the other (row-wise relative ranking). Comparing the 2009 3 Year data (off your wonderful website) vs. 2000 CTPP would seem to have merit. See below:
Are the changes consistent with what is known about the economic and development change in the area? Observed traffic flows (yet more data) and changes in the flows over time? What’s missing or considered incompletely in each dataset? Do the differences in the dataset suggest I need to use them to inform decision-making differently.
All fair and good comparisons (and questions) that help provide me some level of insight both into data differences and change. For a “real-world” comparison of two different dataset that has made a difference in understanding, think about the release and subsequent re-release of the NHTS based on comparisons made between its findings and the NTD for US transit ridership. The comparison highlighted additional considerations that would need to be included in the weighting process for NHTS. Without the comparison, the suitability of NHTS for certain transit analyses would be in question.
The more comparisons we make and questions we ask the better the data gets and the better the understanding of its limitations. Of course, if we blindly use any data, caveat emptor.
My 2 cents.
W
-----Original Message-----
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Today's Topics:
1. RE: 2000 and 2006-08 work trip comparison question.
(Weinberger, Penelope)
2. RE: 2000 and 2006-08 work trip comparison question.
(Kendra Watkins)
----------------------------------------------------------------------
Message: 1
Date: Mon, 31 Jan 2011 10:41:28 -0500
From: "Weinberger, Penelope" <pweinberger@aashto.org>
Subject: RE: [CTPP] 2000 and 2006-08 work trip comparison question.
To: <ctpp-news@chrispy.net>
Message-ID:
<94A99461953E3341B89642B00D5C0B7D0705A4B4@AASHTO-MAIL.aashto.local>
Content-Type: text/plain; charset="us-ascii"
The CB does not recommend comparing an ACS based data set to a CB Long
Form based data set. The 2000 data represent a point in time estimate,
the ACS data represent a period estimate. Furthermore, the Census
Bureau recommends not comparing period estimates with overlapping years.
Penelope Weinberger
CTPP Program Manager
AASHTO
202-624-3556
http://ctpp.transportation.org/Pages/default.aspx
<http://ctpp.transportation.org/Pages/default.aspx>
It's just as bad to not make a plan as to blindly follow the one you
already have.
From: ctpp-news-bounces@chrispy.net
[mailto:ctpp-news-bounces@chrispy.net] On Behalf Of Seidensticker, Dan
Sent: Friday, January 28, 2011 4:18 PM
To: (ctpp-news@chrispy.net)
Subject: [CTPP] 2000 and 2006-08 work trip comparison question.
We downloaded the2006-2008 ACS county-to-county worker flow for Dane
County, Wisconsin from http://ctpp.transportation.org/Pages/3yrdas.aspx.
The question we now have...can that data be compared to the
county-to-county 2000 CTPP work trips to determine any statistically
significant increase/decrease? If so, how would one calculate the
margin of error?
Dan Seidensticker
GIS Specialist
Madison Area Transportation Planning Board:
A Metropolitan Planning Organization (MPO)
City of Madison Planning Unit
121 S. Pinckney Street, Suite 400
Madison, WI 53703
Voice: 608-266-9119
Fax: 608-261-9967
Email: dseidensticker@cityofmadison.com
www.MadisonAreaMPO.org <http://www.madisonareampo.org/>
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Message: 2
Date: Mon, 31 Jan 2011 09:05:15 -0700
From: "Kendra Watkins" <kwatkins@mrcog-nm.gov>
Subject: RE: [CTPP] 2000 and 2006-08 work trip comparison question.
To: <ctpp-news@chrispy.net>
Message-ID:
<A09F069636CC904E94E0D2BEA80A1468017DBBF2@mrcog.mrcog-nm.gov>
Content-Type: text/plain; charset="us-ascii"
This is interesting. I recall hearing this guidance in the past. However
on the Census website on the ACS page it specifically states;
"Generally, you can compare American Community Survey (ACS) 3-year and
5-year estimates with Census 2000 data. There are differences in the
universe, question wording, residence rules, reference periods, and the
way in which the data are tabulated which can impact comparability."
The qualifier in the second sentence addresses the conflict (different
methods, time periods etc) but I can't find anywhere on the ACS pages
where the Census recommends we not compare ACS to decennial Census. And
when I search by subject the Journey to Work topic states that I can
'Compare' it to the 2000 Census.
It does specifically state not to compare overlapping years on multiyear
estimates.
Kendra Watkins
Senior Data Analyst
Mid-Region Council of Governments
809 Copper Ave. NW
Albuquerque, NM 87102
Phone: (505)724-3601
Fax: (505)247-1753
Email: kwatkins@mrcog-nm.gov <mailto:tgaudette@mrcog-nm.gov>
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From: ctpp-news-bounces@chrispy.net
[mailto:ctpp-news-bounces@chrispy.net] On Behalf Of Weinberger, Penelope
Sent: Monday, January 31, 2011 8:41 AM
To: ctpp-news@chrispy.net
Subject: RE: [CTPP] 2000 and 2006-08 work trip comparison question.
The CB does not recommend comparing an ACS based data set to a CB Long
Form based data set. The 2000 data represent a point in time estimate,
the ACS data represent a period estimate. Furthermore, the Census
Bureau recommends not comparing period estimates with overlapping years.
Penelope Weinberger
CTPP Program Manager
AASHTO
202-624-3556
http://ctpp.transportation.org/Pages/default.aspx
<http://ctpp.transportation.org/Pages/default.aspx>
It's just as bad to not make a plan as to blindly follow the one you
already have.
From: ctpp-news-bounces@chrispy.net
[mailto:ctpp-news-bounces@chrispy.net] On Behalf Of Seidensticker, Dan
Sent: Friday, January 28, 2011 4:18 PM
To: (ctpp-news@chrispy.net)
Subject: [CTPP] 2000 and 2006-08 work trip comparison question.
We downloaded the2006-2008 ACS county-to-county worker flow for Dane
County, Wisconsin from http://ctpp.transportation.org/Pages/3yrdas.aspx.
The question we now have...can that data be compared to the
county-to-county 2000 CTPP work trips to determine any statistically
significant increase/decrease? If so, how would one calculate the
margin of error?
Dan Seidensticker
GIS Specialist
Madison Area Transportation Planning Board:
A Metropolitan Planning Organization (MPO)
City of Madison Planning Unit
121 S. Pinckney Street, Suite 400
Madison, WI 53703
Voice: 608-266-9119
Fax: 608-261-9967
Email: dseidensticker@cityofmadison.com
www.MadisonAreaMPO.org <http://www.madisonareampo.org/>
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