[CTPP] Some more points

Thanks to everyone who commented on my comments. Regarding ACS data delivery, there is a plan in the works which is going to be tested this year. It's called "Tier 3," referring to American FactFinder (tier 1 is the profiles, and tier 2 is the summary file tables, both now available). In Tier 3, the idea is that the user could specify the precise geography and precise cross-tabulation(s) desired, and the system will check to see if the requested table meets confidentiality criteria before delivering it. The table would run off the basic 2000 census record. If Tier 3 works out, it would probably be extended to the ACS files. Thus, for example, a run could be done for a group of tracts with population 65K or higher. This OUGHT to include a standard profile for the custom geography. I definitely agree with the idea of sub-MCD ACS tabulation areas--these are not PUMAs because they're not for microdata. This is an idea to be worked on for the future. I am skeptical about block group data. They have never been very reliable anyhow, and are mostly important to the private sector because they permit more precise aggregation in what I call radius analyses (1 mile circle, three mile circle, etc.) The long form data at the individual block group level have very high sampling and non-sampling error rates. In addition, block groups are largely "accidental" geography, because the lines between them are most often arbitrary and not based on any real-life criteria. Tracts (and TAZs), on the other hand, are deliberately drawn to meet local criteria, or they should be. I think it would serve us all better to refer to TAZs as tract-equivalents rather than block-group equivalents. In areas without high employment density, that's what they are. I don't think a fight over block group data will serve anyone well as this point. The "rolling average" means that while data released at the tract level in 2008 were collected in 2003-7, the 2009 release will include 2004-8 data, and so forth. One of the most important things about the ACS is that it is in the field on a 12 month basis. This is a distinct difference from the census long-form, which is collected as of April 1 (at least in theory) and for which the income data represent the previous calendar year. In ACS, the income data will reflect the past 12 months. Mobile populations will be enumerated where they are at any given time, which means that a town like Gainesville, FL, which has a much lower population count in the summer than in the winter (40K to 100K) will show up with less than 100K population in the ACS. Analysis of these various differences is one of the main purposes of the supplementary surveys, especially the C2SS in 2000. Elaine--good luck on getting 14 tables on the TAZ/TAZ matrix. I'm pretty skeptical given the current climate, especially since the fact that the data go only into models doesn't carry much weight with the DRB. I will be interested to see what happens. I would recommend, though, that you consider giving up some of the detail in the interest of having the counts. About the rule of 100: that is the arbitrary cutoff for presentation of data on SF2. See http://www.census.gov/Press-Release/www/2001/sumfile2.html. SF4 will probably be higher. But again, remember, that the cutoff on these files is designed for the presentation of data for these small race/ethnic groups. It makes sense not to deliver 47 tables for a population group with only 35 (or 99) people in a given geographic area such as a tract or small MCD. You can always look at a higher level of geography, such as the county, to get these characteristics for the (perhaps slightly) larger population count for the group. An important point about SF2, and what I said above, is that the file is PUBLIC. It will be out there on AFF and anyone can look at it. The case needs to be made that the CTPP, data for TAZs, is NOT PUBLIC in the same sense. Eventually they're going to have to work out licensing agreements or something similar to handle this problem. Right now, we're in the crosshairs of the problem without good decisions having been made. As I said before, eternal vigilance is required. Patty Becker Patricia C. (Patty) Becker 248/354-6520 APB Associates/SEMCC FAX 248/354-6645 28300 Franklin Road Home 248/355-2428 Southfield, MI 48034 pbecker(a)umich.edu