Re: [CTPP] Data detail

Let me try to address some of the issues that Liz Hartmann raises: Over the past two or three years, the concerns about privacy and confidentiality in data release have grown exponentially. At the census bureau, this issue exploded two years ago with the question of what would be on the Public Use Microdata Sample file (PUMS). The original plan

have, essentially, made the file useless. After a user meeting convened

the Population Division at the bureau, and a LOT of internal negotiating, the final outline for the 2000 PUMS file is quite reasonable. I have no problem with top coding and rounding, because, in fact, the data are not reliable at the per minute level for journey to work, or at the details of very high income levels. My only problem is with the 100,000 cutoff, but it was clear that we could not fight that this time around. The long-form data are weighted to represent the total population in publications and summary files. You can see those weights on the PUMS file. Theoretically, they would be 6 to 1, since the sample is 1 in 6,

a lot of things can make them different from that. I have not heard what the cutoff level is going to be on SF4 for the long form data; the

point is that we won't have any cutoff level on SF3. Remember, again,

SF2 and SF4 are a completely different concept than they were in 1980/90. They have exactly the same tables as SF1/SF3, but are iterated for the small race/ethnic groups such as Indian tribes when there is a big enough N to do so. That makes perfect sense to me. The important point that needs to be made for TAZ files (especially the

to TAZ) is that these files are used only in modeling. No one makes a printed (or web-based) report out of them! We all know, or should, that the data are very, very thin, and thus really are not very reliable. But there are so many TAZ pairs that the model handles the problems--or at least I hope it does. I think there is a reasonable chance that we will be able to get the CTPP tables needed for transportation planning when the ACS reaches its full five-year cycle, planned for 2008. The data will still be thinner than long-form data; we will have a chance to measure what all that means for geographic areas larger than tracts/TAZs as the one year, two year, and three year accumulations become available. We are supposed to get

tables for areas of 65,000 or more, and two-year data for areas of 30,000 or more. That's probably enough for the districts used in the models. "Is there room for collapsing across some of the "people categories" in order to have data for the smaller geographic levels? How much would that cost in dollars and timeliness?" That's already handled in the design of the tables for any given product, including the CTPP. The TAZ/TAZ file

nothing but the count of workers, right? We get, or impute, characteristics from the wider data set that's on the TAZ of residence and TAZ of work files. Yes, I completely agree with "But I'd hate to lose the baby with the bathwater. There's so much to be gained from this incredible data source. It's one of the best things going (in my opinion), and crucial to good Planning." Personally, I plan to remain in the fight as long as possible. We will have to deal with it product by product. Two weeks

I attended a DC conference on privacy and confidentiality. Of perhaps 275 people there, at least 240 were from federal agencies. There were very

users. We have to make sure the user community is heard from. I will be happy to work with the CTPP community on this. I am a demographer rather than a transportation planner, but have more experience than most demographers with the CTPP (and UTPP) and the use of these data. 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