RE: [CTPP] 2004 ACS Data Release

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@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.