Transporation Data Users,
The Census Bureau has provided early release of selected workplace based
tables for areas affected by Hurricanes Katrina and Rita. Included in this
release are the following tables:
B08406. Sex of Workers by Means of Transportation for Workplace Geography,
2004
B08526. Means of Transportation to Work by Industry for Workplace
Geography, 2004
B08528. Means of Transportation to Work by Class of Worker for Workplace
Geography, 2004
B08534. Means of Transportation to Work by Travel Time to Work for
Workplace Geography, 2004
These tables are being released for States, Counties, Places, and
Metropolitan Statistical Areas for areas of 250,000 or more residents in
Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, Tennessee, and
Texas. These tabulations are produced to provide estimates of workers at
the location of their workplace. Estimates of counts of workers at the
workplace may differ from those of other programs because of variations in
definitions, coverage, methods of collection, reference periods, and
estimation procedures. The ACS is a household survey which provides data
that pertains to individuals, families, and households.
This data for AL, LA, and MS can be found on the Hurricane Data link off
the main Census page at www.census.gov or directly at
http://www.census.gov/Press-Release/www/2005/katrina.htm. Currently on the
Katrina tab, there is a Transporation Section which contains the Workplace
tables. This site will be updated to reflect the damage done by Rita, so
check back on the "Rita tab" for more information later.
The complete tables can be found on AmericanFactfinder
(www.factfinder.census.gov), marking the first time data tabulated at the
Workplace Geography is included on American FactFinder.
The remainder of the states geography will be released early next year as
indicated in the current schedule for 2004 ACS data.
Clara Reschovsky
US Census Bureau
CTPP Update
9/28/2005
A. Distribution of Part 3 discs with CAT software and .ivt data files
We have completed our distribution of all the Part 3 discs containing the
CTPP Access Tool (CAT) software and data in that browser's .ivt format.
This included two higher-capacity CDs (VA and OH) and three DVDs (TX, CA,
and NY-NJ-PA). However, late in the distribution process some problems were
discovered in a few of the Part 3 .ivt tables, so the CDs and DVDs we have
distributed so far all contain some erroneous Part 3 data. See item B below
for an explanation of the error and information regarding a rerun of the
bad Part 3 tables.
B. Error in Part 3 tables
As noted in Clara Reschovsky's note to the CTPP listserve on 7/25/2005, an
error was discovered in some of the Part 3 tables in the .ivt format
contained on the software CDs and DVDs. The data distributed last year in
ASCII format do not contain the error. The error in the .ivt files is a
result of the vendor incorrectly reading the ASCII files into the browser's
format.
The error affects three tables in Part 3:
1) Table 3-08. Mean travel time by means of transportation to work (8) and
time leaving home to go to work (4)
2) Table 3-09. Median travel time by means of transportation to work (8)
and time leaving home to go to work (4)
3) Table 3-14. Aggregate travel time by means of transportation to work (8)
and time leaving home to go to work (4)
These three tables have been corrected and new files have been rerun by the
vendor. We are in the process of bundling the corrected tables into a small
number of Part 3 correction CDs that we will begin to distribute next
month. Therefore, all State Departments of Transportation and Metropolitan
Planning Organizations will be receiving one more CD from us, containing
the corrected .ivt format tables for Part 3. Note that the correction CDs
will also contain reruns of two other Part 3 tables, to correct an income
label problem as described in item C below.
C. Error in CAT household income labels for some variables in Parts 1, 2,
and 3
An error has been discovered in some income category labels being used in
the CAT software, affecting data in the browser for all three Parts of the
CTPP. The data have been tabulated according to the labels shown in
Appendix F of the CTPP documentation, but the CAT browser software is using
labels that show some incorrect income category breaks. The most detailed
household income variable (with 26 categories) is correct and not affected
by the error.
The variables affected are:
* Household income in 1999 (11), used in Part 1 (tables 30, 39, 75, 76, 79,
82) and Part 2 (tables 30 and 39)
* Household income in 1999 (9), used only in Part 3 (table 5)
* Household income in 1999 (5), used in Parts 1 and 2 (tables 42, 43, 44
in each part) and in Part 3 (table 7).
The Part 3 correction CDs that we will distribute in October will contain
new versions of tables 5 and 7 with corrected household income labels for
those two tables. However, we will not be producing corrected versions of
the Part 1 or Part 2 tables that contain erroneous income category labels
in the CAT software.
The correct household income labels may be found in Appendix F of the CTPP
documentation and are also shown below. The labels preceded with asterisks
below are correct and should be substituted for the incorrect labels
provided in the browser.
Household income in 1999 (11)
Total, Household income in 1999 (11)
Less than $10,000
$10,000-$14,999
***$15,000-$29,999
***$30,000-$39,999
***$40,000-$49,999
***$50,000-$59,999
$60,000-$74,999
$75,000-$99,999
$100,000-$124,999
$125,000 or more
Household Income in 1999 (9)
Total, Household income in 1999 (9)
Less than $15,000
***$15,000-$29,999
***$30,000-$39,999
***$40,000-$49,999
***$50,000-$59,999
$60,000-$74,999
$75,000-$99,999
$100,000 or more
Household Income in 1999 (5)
Total, Household income in 1999 (5)
***Less than $30,000
***$30,000-$49,999
***$50,000-$74,999
$75,000 or more
Any questions concerning these issues should be referred to Clara
Reschovsky (clara.a.reschovsky(a)census.gov) or Phil Salopek
(phillip.a.salopek(a)census.gov). Thank you.
Last week, two more comments on ACS 2004 data were posted on this network.
The first is from Ken Cervenka who stated that the concept of continuous
surveying appears very sound. I completely agree, we all love to have
current data for transportation planning. Unfortunately, the proposed ACS
program will not provide us with accurate estimates that we can use. Based
on DVRPC analysis, the sampling and nonsampling errors in the ACS data are
very large, and the CB simply cannot produce TAZ data comparable to those
obtained from the long-form of Census 2000. There are many reasons for this
statement, including the ACS sample size is smaller than that of the
long-form of the decennial census; it is almost impossible to improve the
quality of various data sets to estimate the moving five year average; and
the ACS sample does not include group quarters population. As you stated
correctly, the ACS approach requires not only sufficient sample sizes, but
good annual weighting factors at the sub-county level. Re-weighting ACS
samples by sub-county estimated population will not improve the quality of
ACS data greatly. The CB would argue correctly that sub-county population
estimates have larger errors than those at he county level. Many of the
variables used by the CB to estimate demographic data, such as immigration
and vital statistics, are only available at the county level. In addition,
bias in selecting the ACS samples, large non-response rates from certain
population groups, and lack of large marketing programs to promote the ACS
and enhance the quality of data collection and processing, are additional
reasons for the large errors in the ACS data.
Sam Granato wrote that there is no need to even think about reviving the
long-form because Congress has not forgotten yet the outcry from
bureaucrats and people in 2000. Apparently, he is not impressed by the
quality of either the long-form or the ACS data, and wants to develop his
models based on SF1 data and secondary source information. I suggested
bringing back the long-form because of many reasons, including the
following:
1. There are large errors in the ACS data and the data cannot be corrected
easily or used for modeling and traffic analysis. There are no solid basis
for correcting the ACS estimates, such as census population counts;
2. The errors in the long-form data are much smaller than those in the ACS
data. The errors can be corrected by data users based on SF1, SF3, and
other census data. For example, the DVRPC region contains 9 counties in
Pennsylvania and New Jersey, 355 municipalities and 1912 traffic analysis
zones. The evaluation of CTPP data indicated that the population of 9
municipalities was erroneous, the employment in 15 percent of the zones was
not coded correctly, and only 1 zone was not located correctly. The data in
Tables 3-03 through 3-07 in Part 3 of CTPP cannot be used, not because of
major errors in the long-form data, but because of an arbitory decision by
the CBs Disclosure Review Board regarding rounding and disclosure
threshold;
3. The cost of the long-form is lower than that of ACS. In the late 1990s,
the CB stated that the cost of ACS is much lower than that of the long-form,
but in May 2005, it stated in Irvine, CA that the cost of ACS is equal to
the cost of the long-form data. Since the ACS sample size is about 70
percent of the long-form sample size, the ACS cost is actually about 30
percent higher;
4. According to the CB, Census 2000 was very successful because Congress was
interested in accurate population counts, which required the development of
several expensive marketing and technical programs to enhance methods of
data collection and processing and quality control measures. Most of these
programs are not being implemented in the ACS program;
5. Based on DVRPC experience, the errors in data from secondary sources
are higher than those in the CTPP. Also, some variables we use in modeling
are not even available. For example, the CTPP is the only source for
employed persons by place of residence and place of work at the TAZ level.
To collect demographic and employment data at the TAZ level will cost
millions of dollars. The long-form data are free. Because of this, DVRPC
has decided to depend on census data for regional and transportation
planning studies. Although not perfect, the responses to the long-form are
the best source available to us for various transportation studies; and
6. Many planners remember that the CB wanted to delete the long-form from
Census 2000, but could not do it because of the outcry of some bureaucrats
from FHWA, FTA, OMB, state DOTS, and MPOs. With the ACS Program, Congress
is now getting the outcry from the people annually, and some members prefer
to hear all of the outcrying in the decennial census year. I think that the
CB is completely capable of producing quality data in Census 2010, including
the data we need for the transportation planning. After all, the CB has
been doing it for 40 years. In order to produce quality data in Census
2010, the CB should improve its nonsampling procedures, call back, or
reinterview some of those who do not respond to the long-form questions,
develop an accurate geocoding of the place of work addresses, continue its
successful public relations and marketing programs, change rounding rules,
and eliminate the disclosure threshold.
Just a note to let Census Bureau & USDOT folks know that the CTPP Part
3 DVD for California was shipped 9/12/05 and was received in our offices
on 9/19/05.
Question: When will the CTPP CDs and/or DVDs be available from BTS?
Will this be on the BTS Transtat site, or elsewhere?
http://www.transtats.bts.gov/
Thanks in advance,
Chuck P.
**************************************************************
Charles L. Purvis, AICP
Principal Transportation Planner/Analyst
Metropolitan Transportation Commission
101 Eighth Street
Oakland, CA 94607-4700
(510) 817-5755 (office) [new, 8/1/05]
(510) 817-7848 (fax) [new, 8/1/05]
www: http://www.mtc.ca.gov/
Census WWW: http://www.bayareacensus.ca.gov/
**************************************************************
No point in even thinking about reviving the long form. I'm sure our
Congress folk haven't forgotten yet the outcry they got not from us
bureaucrats but from "real people" back in 2000. I don't even recall long
form data being that great either - even by 1990 the non-response and
obvious mis-response were getting pretty high. I'm at the point now where
due to this plus the timeliness of CTPP I'm developing metro travel models
virtually all from SF1 and "secondary source" information, with long-form
data only for control totals or relative adjustments to the totals from
other sources. I'd rather see the Census Bureau concentrate first on
getting the short-form numbers and the geography right, that'll be plenty
enough of a challenge in 2010 and beyond.
Sam Granato
Ohio DOT, Office of Technical Services
1980 W. Broad Street, Columbus, OH 43223
Phone: 614-644-6796, Fax: 614-752-8646
"I think there is some methodology in my travels." - George W. Bush
Of all the things that you outlined for alternatives to replace the ACS, I
would say bring back the long-form. I know it is not easy to reverse the
decision that was made by the CB two years ago. Although not perfect, the
responses to the long-form will be more reliable because it will be
conducted with the decennial census, which is respected by almost everyone
in the country. I think that FHWA should take the lead in promoting this
effort and tell the country that the ACS data are not acceptable for the
transportation community since the margin of error is very large. I
really
don’t know the effective channels of communication to have the long-form
back in Census 2010. But I think the ACS issues should be brought to the
attention of decision makers within AASHTO, APTA, NARC, TRB, Public Data
Users, 2010 Census Advisory Committee, AMPO, 2010 Census Advisory
Committee,
AMPO, House Subcommittee on the Census, and other organizations. Of
course
political pressure is always needed. The other options you outlined are
not
really alternatives to the long-form. Improvements to the ACS county
program will help a little but won’t solve the problem. Large surveys
similar to the surveys conducted in the 1950's and 1960's are out of the
question.
Hello,
As is most likely the case for many other lurkers on the CTPP listserv, I have been reading the recent slew of ACS-related emails with great interest. Exactly what to make of all this--I am still not sure.
Conceptually speaking, the ACS concept of "continuous surveying" with permanent/experienced Census Bureau staff, as opposed to once-every-10-years surveying with a large group of temp employees, appears very sound. Even the idea of a "moving five-year average" to get a finer level of area-to-area detail sounds both workable, better, and timely than what we could ever get in the past. Once a lot of statistical analysis has been performed, I would expect our leading university researchers to come up with useful ways to turn various sets of "moving five year averages" into reasonable specific-year datasets that would be adequate for use with our future local household survey expansions, population synthesis procedures for travel microsimulations, and basic "so this is what is happening in our region" data summaries.
Unfortunately, the ACS approach requires not only sufficient sample sizes for any given year, but a good annual weighting (expansion) process to deal with sub-county geographic and other biases. If I am understanding things correctly, the only weighting to be applied will be at the County level? Maybe I am missing something, for I don't see how this will result in anything but much too much year-by-year variation in household characteristics--it puts way too much pressure on an underlying implicit assumption that the number of households in a County that wind up in each year's dataset are truly representative households for not only the County, but any future sub-County disaggregations that are prepared. I suspect this is why some folks have been noting some big year-by-year changes in important household statistics (autos per household, average household size, etc.) that may not be reflecting real-world annual changes.
I can certainly understand some of the difficulties that would be encountered, but it seems like some modified approach is needed to re-weight the yearly Household ACS samples within Counties by something other than a single county-specific factor. If this was a Year 2000 small-sample local household travel survey we would be able to correct for the most significant within-County response biases by using the Year 2000 Census data as the real-world "truth" for coming up with household-specific weighting factors. But it's not clear what source could be used for a more realistic/useful weighting of annually-collected ACS records. It's not the current ACS sample size that bothers me (although I will be distressed if the sample size should ever get reduced from current levels), but rather the ACS weighting/expansion procedures.
Or...maybe I am missing some important point about the ACS weightings, for which I will actually be grateful to be publicly corrected. Just call me, "perplexed in Dallas".
Ken Cervenka
NCTCOG
(Dallas-Fort Worth MPO)
-----Original Message-----
From: ctpp-news-bounces(a)chrispy.net
[mailto:ctpp-news-bounces(a)chrispy.net]On Behalf Of Richard Lin
Sent: Tuesday, September 20, 2005 8:31 PM
To: ctpp-news(a)chrispy.net; tzakaria(a)dvrpc.org;
Elaine.Murakami(a)fhwa.dot.gov; TMarchwinski(a)njtransit.com
Subject: RE: [CTPP] 2004 ACS Data Release
Dear T,
I completely agree with your comments on the serious limitations
of ACS data. Comparing to your desire to apply the ACS data for
transportation, I am very disappointed about the quality and limitations
of ACS to serve as reference data for evaluating our annual county and
municipal estimates of population and households. However, there are
many other data users out there hoping to get timely demographic
characteristics for making decisions involving either to spend money or
to get money. Less accurate statistics information is still better than
no information for decision making.
Sample statistics from the decennial census long form (from 1/6 of
households or 17 million household samples in Census 2000) indeed are
very much better and reliable (accurate) than that from the 838,000
samples from the 2004 ACS survey in a single year. Without the 2004 ACS
data, we can only depend on the Census 2000 sample statistics. Do you
like that? That is your choice. If so, just don't bother about the ACS
survey data for transportation applications. I am still hope to find
something worthwhile from the annual ACS survey data to check on the
annual estimates of population and households. It is still better than
the March Supplement CPS (Current Population Survey) data which only
contain about 800 (household) samples for Colorado. As of 7-1-2004
Colorado has more than 2,026,000 households. Comparing to CPS, I
appreciate very much to have ACS.
How about canceling the ACS program and campaigning to re-install
Long Form for Census 2010? You all know that if the Senates do not fund
or under fund the ACS test programs for year 2006 and the years after,
it is highly likely that the Census Bureau has to abandon ACS program
and request funding to work on Long Form for 2010 Census. How many of
you would like to see that happen?
>>> <TMarchwinski(a)njtransit.com> 9/17/2005 12:51 PM >>>
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.
-----Original Message-----
From: ctpp-news-bounces(a)chrispy.net
[mailto:ctpp-news-bounces(a)chrispy.net] On Behalf Of Richard Lin
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
Dear All,
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
PM >>>
Dear Zak,
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
2.9
Streetcar/trolleycar+ 195 0.1 1,168 0.8
Railroad or ferry 6,105 4.0 8,795
5.7
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.
Elaine
FHWA Office of Planning
Dear T,
I completely agree with your comments on the serious limitations
of ACS data. Comparing to your desire to apply the ACS data for
transportation, I am very disappointed about the quality and limitations
of ACS to serve as reference data for evaluating our annual county and
municipal estimates of population and households. However, there are
many other data users out there hoping to get timely demographic
characteristics for making decisions involving either to spend money or
to get money. Less accurate statistics information is still better than
no information for decision making.
Sample statistics from the decennial census long form (from 1/6 of
households or 17 million household samples in Census 2000) indeed are
very much better and reliable (accurate) than that from the 838,000
samples from the 2004 ACS survey in a single year. Without the 2004 ACS
data, we can only depend on the Census 2000 sample statistics. Do you
like that? That is your choice. If so, just don't bother about the ACS
survey data for transportation applications. I am still hope to find
something worthwhile from the annual ACS survey data to check on the
annual estimates of population and households. It is still better than
the March Supplement CPS (Current Population Survey) data which only
contain about 800 (household) samples for Colorado. As of 7-1-2004
Colorado has more than 2,026,000 households. Comparing to CPS, I
appreciate very much to have ACS.
How about canceling the ACS program and campaigning to re-install
Long Form for Census 2010? You all know that if the Senates do not fund
or under fund the ACS test programs for year 2006 and the years after,
it is highly likely that the Census Bureau has to abandon ACS program
and request funding to work on Long Form for 2010 Census. How many of
you would like to see that happens?
>>> <TMarchwinski(a)njtransit.com> 9/17/2005 12:51 PM >>>
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.
-----Original Message-----
From: ctpp-news-bounces(a)chrispy.net
[mailto:ctpp-news-bounces(a)chrispy.net] On Behalf Of Richard Lin
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
Dear All,
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
PM >>>
Dear Zak,
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
2.9
Streetcar/trolleycar+ 195 0.1 1,168 0.8
Railroad or ferry 6,105 4.0 8,795
5.7
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.
Elaine
FHWA Office of Planning
-----Original Message-----
From: ctpp-news-bounces(a)chrispy.net
[mailto:ctpp-news-bounces(a)chrispy.net]On Behalf Of Thabet Zakaria
Sent: Tuesday, September 13, 2005 6:54 AM
To: ctpp-news(a)chrispy.net
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
ctpp-news(a)chrispy.nethttp://www.chrispy.net/mailman/listinfo/ctpp-news
- Richard Lin, Ph.D.
Demographer
Colorado Division of Local Government
(303)866-4989, fax (303)866-2660
richard.lin(a)state.co.us
_______________________________________________
ctpp-news mailing list
ctpp-news(a)chrispy.nethttp://www.chrispy.net/mailman/listinfo/ctpp-news
After responding to the points raised by some of my colleagues last week
about the ACS 2004 data, I have received two more comments. The first one
is from Richard Lin, who is hoping that the quality of the ACS data by
Census 2010 will be equal or even better than that of the long-form. This
is not possible because the proposed larger sample size of 2005-2009 (Full
Nationwide Implementation) is about 70 percent of the sample size of the
long-form. Even if Congress approves funding for five years as requested by
the CB, the quality of the ACS data will be lower than the census long-form
because of many other reasons, including the ACS sample is weighted to an
estimated population rather than census, might not include group quarters
population, excludes the impacts of significant discontinuities in
population and employment characteristics, and is not conducted in one year.
In addition, the CB is promising to provide us with TAZ or Census Tract
level data after five year accumulation of ACS data. According to sampling
theory, the sampling errors in the ACS data at the zonal level will be much
greater than that at the county level. We all love to have accurate current
TAZ level data for our planning studies but this wont happen because of the
limitations of the proposed ACS methodology and data collection procedures.
Finally, I would like to ask this question. If you are working for the City
of Oakland, CA and you know that the City is growing, which population
number would you prefer for 2004: Census 2000 of 399,000 or ACS estimated
number of 365,000?
Glen Ahlert suggested to perform a liner regression on the annual ACS data
with respect to year for the areas that are undergoing continual population
or employment growth. Then interpolate or extrapolate to the year of
interest, than to average the annual ACS data. He also stated correctly
that regression analysis wont be reliable for areas that experienced
significant discontinuities in land use and transportation development. I
dont think the CB will accept such a method because it does not work for
the whole country.
For the majority of geographic areas, especially those expected to be
undergoing continual population growth or other demographic changes at a
relatively steady rate, it may be better to perform a linear regression
on the annual ACS data with respect to year, then interpolate or
extrapolate to the year of interest, than to average the annual ACS
data. Obviously there are other areas that have experienced significant
discontinuities in population or demographic characteristics for which
this method would not be very reliable, but then neither would using
multi-year ACS averages.
Glen Ahlert
Director
Lee County MPO
(239) 338-2550 ext. 224
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.
-----Original Message-----
From: ctpp-news-bounces(a)chrispy.net [mailto:ctpp-news-bounces(a)chrispy.net] On Behalf Of Richard Lin
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
Dear All,
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
PM >>>
Dear Zak,
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
2.9
Streetcar/trolleycar+ 195 0.1 1,168 0.8
Railroad or ferry 6,105 4.0 8,795
5.7
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.
Elaine
FHWA Office of Planning
-----Original Message-----
From: ctpp-news-bounces(a)chrispy.net
[mailto:ctpp-news-bounces(a)chrispy.net]On Behalf Of Thabet Zakaria
Sent: Tuesday, September 13, 2005 6:54 AM
To: ctpp-news(a)chrispy.net
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
ctpp-news(a)chrispy.nethttp://www.chrispy.net/mailman/listinfo/ctpp-news
- Richard Lin, Ph.D.
Demographer
Colorado Division of Local Government
(303)866-4989, fax (303)866-2660
richard.lin(a)state.co.us _______________________________________________
ctpp-news mailing list
ctpp-news(a)chrispy.nethttp://www.chrispy.net/mailman/listinfo/ctpp-news
