Hello:
In late August 2006, the US Census Bureau (CB) released the
2005 American Community Survey (ACS) data on population, employed persons,
journey-to-work, and many other demographic and employment characteristics such
as income, poverty, employment status, occupation, and industry. These data
are the first from the full implementation of ACS. This email reviews 2005 ACS
data on population and journey-to-work for the
Population Estimates
The 2005 ACS population estimates are limited to household
population only; they exclude group quarters population. To obtain 2005 ACS
population, the CB estimated group quarters population and subtracted it from
the 2005 total population estimates produced as part of the CB’s
Population Estimates Program (PEP). A comparison of 2005 CB population
estimates with those estimated by DVRPC shows that the CB estimates are very
close to DVRPC estimates. The differences between the two sets of estimates
for six counties are less than 2.5 percent. The CB estimates for two suburban
counties are overestimated slightly and one (
An analysis of the 2005 census estimates of group quarters
population shows that none of the nine estimates is reasonable. Group quarters
population are either overestimated or underestimated. For example, group
quarters population for
Although the magnitude of group quarters population is
generally small, it increased the margin of error in the ACS household
population significantly. Also, the erroneous group quarters population
increased the margin of error in the 2005 ACS economic characteristics, such as
the number of workers and means of transportation to work. Affected the most
are counties with large group quarters population such as
Journey-to-Work
A review of the 2005 ACS journey-to-work by means of
transportation indicates that the margin of error in the estimates is very
large. Also, the CB could not develop all estimates for
Average Travel Time
The 2005 ACS commuter travel time in the region is 28.3
minutes. This value indicates that the average commuter time has declined
slightly between 2000 and 2005 (28.6 vs 28.3). It is interesting to note that
the 2004 ACS travel time increased between 2000 and 2004 (28.6 vs 29.1
minutes). Based on this information, some people may conclude incorrectly that
commuters’ travel time increased from 2000 to 2004 and deceased from 2004
to 2005. No conclusions can be drawn based on this information since the
differences between numbers are small and within the margin of error in the
data. Also, the 2000, 2004, and 2005 census data are not comparable. They are
oranges, apples, and lemons. The sample sizes are different and ACS data
exclude group quarters population. Although the 2005 ACS sample size is larger
than the 2004 sample, it is still about 12 percent of that used in Census 2000.
As I have stated last year after the release of 2004 ACS
data, the errors in the ACS estimates are large and the data cannot be
evaluated or corrected easily. There are no accurate data between decennial
Censuses. As Chuck Parvis stated correctly in his analysis of 2005 ACS data,
it is not possible to “Calculate whether or not there is a meaningful
difference between 2000 and 2005....that’s more or less a professional
judgment call.”
In summary, the 2005 ACS data cannot be used for
transportation planning. The CB simply connot produce quality data from the
ACS program comparable to the long-form of Census 2000 due to large sampling
and non-sampling errors. The ACS sample size is too small, the population universe
is estimated, and the data collection procedures are not consistent with Census
2000.
Thabet Zakaria
Deputy Director, Technical Services
190 N.
Phone: 215-238-2885
Email: tzakaria@dvrpc.org
Fax: 215-592-9125