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.