RE: [CTPP] ESRI article on ACS errors

While I haven't waded into the zero-vehicle data as much as some of you I would offer a few observations. The share of zero vehicle households is somewhat misleading as it is sometimes more or at least equally relevant to look at the share of the population that lives in zero vehicle households. That number is about 60% of the share of households and is surprising to folks when they realize the share of population living in zero-vehicle households is quite small. A few years ago there were some national polls about auto ownership/availability for youth and there were some stunning numbers regarding how fast vehicle availability was growing for youth. This is an interesting segment to explore regarding vehicle saturation. With high fuel costs we could have conflicting pressures where high prices spur additional vehicle ownership in order to specialize vehicles, i.e. keep that depreciated SUV for when you need it and buy that small car for commuting. Marginal vehicle ownership costs in the U.S. are modest enough that this trend may offset at least part of any tendency for households to relinquish vehicles due to higher fuel costs. A couple years ago we did some analysis of the consumer expenditure surveys with respect to vehicle availability and found that the highest marginal spending per vehicle occurred in households that had more vehicles than adults. We speculated that it is wealthier households in this situation and that is where vehicle specialization begins. They add that convertible or RV as an extra vehicle. Steven E. Polzin, Ph.D. Center for Urban Transportation Research University of South Florida 4202 Fowler Ave., CUT100 Tampa, FL 33620-5375 813-974-9849 (w) 813-416-7517 (c) polzin(a)cutr.usf.edu http://www.cutr.usf.edu -----Original Message----- From: ctpp-news-bounces(a)chrispy.net [mailto:ctpp-news-bounces@chrispy.net] On Behalf Of Chuck Purvis Sent: Monday, July 28, 2008 11:45 AM To: ctpp-news(a)chrispy.net Subject: RE: [CTPP] ESRI article on ACS errors Michael: Short answer: very well. Long answer: The wording on the ACS vehicle availability question is identical to the Census 2000 question. It's placement in the ACS is between the two housing utility questions (plumbing/kitchen/telephone facilities, and home heating), so these are all the "easy" housing questions before one has to answer the "difficult" housing questions (e.g., how much is spent on x, y, and z....) We've done some county and regional level tabulations of our region's auto ownership patterns, from 1960 to 2006, and the trends do make good sense at both the regional and county level. There are some ups-and-downs in the county-level zero vehicle shares, comparing 2000 to 2005 to 2006, but these may not be statistically significant. (We published this data, released in I believe September 2007, for a November 2007 regional workshop, url: http://www.mtc.ca.gov/maps_and_data/datamart/census/) Our regional share of zero-vehicle households has declined from 19.7% in 1960, to 15.8% in 1970; 12.2% in 1980; 10.5% in 1990; 10.0% in 2000; and then 9.5% in 2005, and 9.2% in 2006. This is for the nine-county San Francisco Bay Area. For San Francisco City, the zero-vehicle household share has decreased from 42.1% in 1960; 39.6% in 1970; 34.6% in 1980; 30.7% in 1990; 28.6% in 2000; and then with the ACS: 31.3% in 2005, but dropping back to 28.6% in 2006 (same as 2000). So, we're anxiously awaiting the 2007 annual ACS data that's scheduled for released next month and September, and then the 3-year period estimates (2005-2007) expected this December. The challenge will be how to analyze and report all of this data in a timely manner, all the while trying to do our "regular jobs."....The other challenge: do we just report the estimates WITHOUT their standard errors necessary in understanding the year-to-year, or period-to-period difference; or do we take the EXTRA time needed to report the estimates WITH the standard errors (adding, or perhaps "delaying" the reporting of the results by say 3 to 6 months? Chuck ************************************************************** Charles L. Purvis, AICP Principal Transportation Planner/Analyst Metropolitan Transportation Commission 101 Eighth Street Oakland, CA 94607-4700 (510) 817-5755 (office) (510) 817-7848 (fax) cpurvis(a)mtc.ca.gov (e-mail) www: http://www.mtc.ca.gov/ ************************************************************** Chuck (or others), In your opinion, how well do you think ACS is estimating Zero Vehicle Households? (or conversely household vehicle ownership?) Michael E. Cline Research Associate Institute for Demographic & Socioeconomic Research The University of Texas at San Antonio 1 UTSA Circle BB 4.06.10 San Antonio, TX 78249-0704 (210)458-6537 f(210)458-6541 michael.cline(a)utsa.edu http://idser.utsa.edu _______________________________________________ ctpp-news mailing list ctpp-news(a)chrispy.net http://www.chrispy.net/mailman/listinfo/ctpp-news