The population in the Mercer County declined by 11,000 during between the 2 surveys (about 9,000 if you use the 2000 Census population). This could explain some of the difference. However, since the confidence intervals overlap for the number of walkers, there is not a statistically significant difference at the alpha =0.10 level. Sample error appears to be the culprit. If alpha =0.05 was used, there would likely be a statistical difference.
Greg Lipton
King County Transit
Seattle, WA
206 263-4673
-----Original Message-----
From: ed christopher [mailto:edc@berwyned.com]
Sent: Tuesday, September 13, 2005 1:02 PM
Cc: ctpp-news@chrispy.net
Subject: Re: [CTPP] 2004 ACS Data Release
Zak raises a lot of issues and I am hopefully that some of the Census folks and
others on this list may be able to help. Needless to say, there is a whole lot of
education that needs to be done when working with these data. Especially when
dealing with year to year changes.
One area that particularly struck me in Zaks work was the comparison of ACS 2000
Mercer county walkers to ACS 2004 Mercer county walkers. When I saw Zak's numbers I
went to Fact Finder to see for myself what may have been happening and this is what
I found. First, Mercer county was not an ACS test site in 2000 so I used the C2SS
data for 2000. Looking at those numbers I got 5,567 walkers (with a low of 2,465
and a high of 8,669) for 2000 and 2,924 (with a low of 1,556 to 4,292) for 2004. Or
put another way 2000 was 5,567 plus or minus 56% while 2004 was 2,924 plus or minus
47%. Becoming even more curious, I checked out 2003 and found 4,303 walkers (with a
low of 2,223 to 6,383). That turned out to be 4,303 walkers plus or minus 48%. So
what does all this mean? I am not quite sure except to say that for 2003 the
overall mode split of walkers was 2.6% with a range of 1.4% to 3.7%. The mode split
of walkers for 2004 was 1.8% with a range of 1.0% to 2.6%. However you slice it,
something is going on but just what???.
Hopefully, the "Guide to Using the ACS" that the Census Bureau is developing and the
NCHRP project to develop a guidebook on using the ACS data will help us plow though
the forest that is apparently growing right before our eyes.
Thabet Zakaria wrote:
> 2004 ACS Data Release by Thabet Zakaria dated September 12, 2005 is
> resubmitted in PDF.
>
> ------------------------------------------------------------------------
> Name: 2004 ACS Data Release.pdf
> 2004 ACS Data Release.pdf Type: Portable Document Format (application/pdf)
> Encoding: base64
>
> ------------------------------------------------------------------------
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--
Ed Christopher
Resource Center Planning Team
Federal Highway Administration
19900 Governors Drive
Olympia Fields, Illinois 60461
708-283-3534 (V) 708-574-8131 (cell)
708-283-3501 (F)
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