New subject: Data detail - ACS Data

23 Jan 2002

Dave:

You raise some excellent points, and I'll try to respond.

Yes, what the CENSUS BUREAU means by areas of 65,000-plus population are places, counties,
MSAs, etc., with at least 65,000+ total population.

But consider the example of BIG CITY, say, BIG CITY in New Mexico with a current
population of 448,607. Now, wouldn't YOU like to split this city into 6 "ACS
Districts" of at least 65,000+ population, where you could then get ANNUAL DATA for
each of these sub-city districts??? (I pitched this idea at our TRB "ACS
Workshop" this past Sunday, January 13th. Census Bureau folks were interested - -
didn't say yes, didn't say no to what I was pushing....)

If we can define PUMAs of 100,000-plus population, then certainly we can also define ACS
districts of 65,000-plus population?

In terms of TAZ-to-TAZ commute flow data, it will be very necessary to aggregate five
years of ACS data in order to get reliable, very small area (tract, taz) data. So, the
first release of "very small area" data from the ACS should be 2008, to
represent aggregated data from 2003-2007.

Block groups. In terms of tract versus block group, I've only seen the Census Bureau
publicly admit to providing tract-level data only. I don't recall us raising the block
group issue at our ACS workshop, but the Census Bureau *was* saying that TAZ data would be
available by 2008 (my USDOT colleagues should correct me if I'm wrong). Since TAZes
are similar in size (population, employment-wise) to block groups, it would make sense to
me that block group ACS data is released in 2008, as well. I totally agree with you about
block group data being made available!!!

I haven't seen any statistical research by Census Bureau staff that discusses the
standard errors of census tract data versus standard error of block group data, based on
5-year accumulation of ACS data. What I have seen is the research that justifies the
65,000+ threshold and thresholds for other multi-year (2-year, 3-year, 4-year, 5-year)
accumulation of ACS data (see ACS web page, paper by Chip Alexander on this particular
issue.)

Also, I don't think the Census Bureau has ruled out (or positively commited TO)
multi-year products other than the five-year census tract data. So, we COULD see 2-year or
3-year or 4-year accumulation of data, if that's what the user community is REALLY
after! Maybe with 6-year or 7-year accumulation of data we get "block groups"?
Who knows? (And whether these multi-year tabs are FREE or COST-REIMBURSABLE is yet another
issue in the "to be determined" column of issues.)

Hopefully (sooner rather than later) our USDOT colleagues will post our powerpoint
presentations from the TRB ACS workshop on our subcommittee's website
(www.trbcensus.com). (nudge, nudge ;-)

Chuck Purvis, MTC

***********************************************
Charles L. Purvis, AICP
Senior Transportation Planner/Analyst
Metropolitan Transportation Commission
101 Eighth Street
Oakland, CA 94607-4700
(510) 464-7731 (office)
(510) 464-7848 (fax)
www: http://www.mtc.ca.gov/
Census WWW: http://census.mtc.ca.gov/
***********************************************

...
 >> David Abrams &lt;dabrams(a)mrgcog.org&gt;
01/23/02 03:36PM >>> This sounds fairly reasonable, but I would like at
least one clarification.
You stated that there would be one-year tables for areas of 65,000 or more
and two-year data for areas of 30,000 or more.  Are these areas defined as
places or counties?  In the same paragraph you referred to a five-year cycle
in a manner that implied that the CTPP was based on five years of data, is
this a correct interpretation?

I am also concerned that the minimum geographic level for sample data
appears to be the tract.  The block group level for sample data has been
very valuable.  Is it correct that we would lose block group level sample
data?

Dave Abrams
Information Services Manager
MRGCOG, Albuquerque, NM

RE: [CTPP] Data detail - ACS Data