Dear Mr. Lin- I disagree with you about census long form vs. ACS. I cannot use the ACS
for any transportation planning analysis except maybe to see where general trends are
going. Even there, looking at NJ data by county, there are some weird changes in mode
data even from year to year. I use the 2000 Census data almost every week, and the ACS,
unless it can get down to a smaller geography, does not do much good. Unless you are doing
some high level comparisons about average travel time or average mode split etc., it
cannot be used for what most transportation planners need, such as trip distribution, mode
split, auto occupancy, vehicle ownership etc. If there is no long form, then we will have
to take what we can from the ACS and combine it with other data, surveys etc.
From: ctpp-news-bounces(a)chrispy.net [mailto:email@example.com] On Behalf Of
Sent: Friday, September 16, 2005 7:48 PM
To: ctpp-news(a)chrispy.net; tzakaria(a)dvrpc.org; Elaine.Murakami(a)fhwa.dot.gov
Subject: RE: [CTPP] 2004 ACS Data Release
We all realize the limitations and quality of the ACS data. Also, we all are seeking
better resolutions. First of all, we hope the Census Bureau gets enough funding to
carrying out ACS operations and to improving the quality of data by accumulating greater
samples. Hope by Census 2010, the quality of the ACS data is equal to or even better than
that of the traditional long form. Without annual ACS survey, we will fall back again to
the once a 10-year long form data availability. Will you prefer still using the Census
2000 Long Form data in 2005 or do you appreciate the limited 2000-2004 ACS data? Without
the annual ACS data, we will go back to the dark again.
The good news is that if the Census Bureau gets funding to continue ACS survey
through Census 2010 then we should have much more reliable and larger sample ACS data for
better quality time series.
With the sampling error variation, we should be more cautious about time series
fluctuations and verify the true changes in numbers such as the Jew Jersey's Mercer
County having lesser workers riding bikes or walk to work (5,450 or 3.5 in Census 2000
comparing to 2,924 or 1.9 in ACS 2004). We should also be cautious when we compare apple
to orange. We may check the data at state (NJ) level by comparing the state's Census
2000 numbers and ACS 2000 numbers to establish a ratio factor for county adjustment for
time series comparison.
>> "Murakami, Elaine"
<Elaine.Murakami(a)fhwa.dot.gov> 9/14/2005 1:39:12
Thank you for providing your opinion on the disutility of the ACS 2004 data for your
applications, and I am glad that others are examining data for their area and are sharing
their findings with the listserv.
My earlier email was sent to CAUTION people who might try to compare 2000 decennial data
to ACS 2004 data. As I said in my earlier email, it is probably better to compare ACS
results to ACS results, than to compare ACS results to decennial census results, however,
results from ACS from 2000 are very limited. The geographic coverage of County level data
from the ACS in 2000 is sparse, which makes comparisons for ACS between 2000 and 2004
possible only in some areas.
The ACS did not go into "full implementation" until 2005, and it will require
multiple years of data collection before data for small areas will be reliable because of
the small samples collected each month and
averaged over time. As Tom Marchwinski pointed out, averaging over
multiple years creates other problems. In 2005, the CB begin differential non-response
follow-up, so that in areas (tracts) with low mail-back responses, there is a greater rate
(1:2 and 2:5 instead of
1:3) made to follow-up non-respondents from the mail-back and CATI portion of the ACS.
Not surprisingly, the areas with low mail-back responses are more likely to be low income,
and higher shares of African American and Hispanic populations. My guess is that this
will cause a shift in numbers between 2004 and 2005, and could impact variables such
as carpooling and transit use and number of vehicles in households.
The Census Bureau recommends that the ACS should be used to describe characteristics, and
not to use it for COUNTS. When I examine the Mercer County NJ data comparing Census 2000
(workers in households) to ACS 2004 (workers in hhlds), I find that about the only thing
to say is that "driving alone" appears to increase from 77 to 78%, and
"carpooling" to decrease from 11 to 10%, "rail" also appears to
increase from 4 to nearly 6%. (Worked at Home is not included in column in the table
below). HOWEVER, this is not taking into account the effects of the different survey
methods, where, generally speaking, the decennial census has a greater share reporting
"carpooling," which is why a BRIDGE from decennial 2000 data is so important.
Thus, it is probably incorrect to say that carpooling is declining.
Mercer County, NJ
Workers in Hhlds Census 2000 ACS 2004
Number Pct Number Pct
Total 153,665 153,041
Drove alone 118,390 77.0 119,597 78.1
2-person CP 13,105 8.5 12,026 7.9
3+ person CP 4,580 3.0 2,722 1.8
Bus/trolley bus 4,585 3.0 4,390
Streetcar/trolleycar+ 195 0.1 1,168 0.8
Railroad or ferry 6,105 4.0 8,795
Bike or Walk* 5,450 3.5 2,924 1.9
Taxi/motorcycle/other 1,255 0.8 1,419 0.9
* 2000 is walk + bike, 2004 is walk only
The county estimates program which is used to weight the ACS data is drawing considerable
fire, as evidenced by the post by Jeffrey P. Levin from the City of Oakland.
Things for State DOTs and MPOs to consider if you feel that the ACS will not provide you
with quality data:
1. Can your organization leverage enough political resources to bring back a Census
"long form" ?
2. Would improvements to the county estimates program make you feel
more comfortable with the ACS results?
3. Should your organization consider conducting a very large sample survey, similar to
the surveys conducted in the 1950's and 1960's where sample sizes of 3 - 5 % of
all households were asked to completed a travel diary? One of the goals of these surveys
was to produce an O/D matrix for a limited number of zones. An area with 1 million
population might have 400,000 households, therefore a 4% sample would be 16,000
households. Let's estimate the cost of a household survey at a conservative $150 per
complete, resulting in a estimate of $2.4 million. Keep in mind that the response rates
to recent regional household travel surveys have been between 25-30%, which is much lower
than the ACS, thus, risking much higher sample bias. Once you get the results, you will
need to determine a method to weight your results for regional totals.
4. Should your organization implement a survey on group quarters population, or do you
believe that the ACS will include group quarters in 2006, as planned.
5. Should you find an alternative data source for home-to-work flows.
Sorry for the long post, and hope that my table comes over without distortion.
FHWA Office of Planning
[mailto:firstname.lastname@example.org]On Behalf Of Thabet Zakaria
Sent: Tuesday, September 13, 2005 6:54 AM
Subject: [CTPP] 2004 ACS Data Release
2004 ACS Data Release by Thabet Zakaria dated September 12, 2005 is resubmitted in PDF.
ctpp-news mailing list
- Richard Lin, Ph.D.
Colorado Division of Local Government
(303)866-4989, fax (303)866-2660
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