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Some Thoughts on Census Adjustment

Groves rules out use of sampling in 2010 census:

President Barack Obama’s pick to lead the Census Bureau on Friday ruled out the use of statistical sampling in the 2010 head count, seeking to allay GOP concerns that he might be swayed to put politics over science. Robert M. Groves, a veteran survey researcher from the University of Michigan, also testified during his confirmation hearing that he remains worried about fixing a persistent undercount of hard-to-reach populations . . . Census officials have already acknowledged that tens of millions of residents in dense urban areas — about 14 percent of the U.S. population — are at high risk of being missed because of language problems and an economic crisis that has displaced homeowners.

Adjusting the census would probably help the Democrats, both in the direct sense increasing the number of Democratic-leaning congressional districts, and in the indirect sense of increasing the political influence, and perceived political inference, of inner cities and ethnic minorities.

My comments:

I have a great respect for Bob Groves, and I would trust his decisions on what to do with the Census more than I would trust my own.

Bob’s statement that “there is simply no time to prepare for it” seems eminently reasonable to me, especially given the cost constraints under which the census operates. On the statistical merits of the issue, I’m pretty sure that adjusted numbers would be better than unadjusted numbers. The census people know what they’re doing, and there are known problems of nonresponse, and, for anything where I care about the damn answer, I’d use their adjusted estimates over the raw numbers.

As a social scientist, I hope the census bureau could release two sets of numbers, one unadjusted for political reasons and one adjusted for those of us who want the most accurate inferences possible.

That said, I’m ignoring a possible indirect effect of adjusting the numbers: If people know that the census will do adjustment, maybe they’ll be less likely to participate in the enumeration in the first place. It’s hard to measure such an effect and, hey, it might be important. I don’t know.

I’m not thinking so much of individuals deciding whether to respond to the census, but rather of the decisions of local jurisdictions, where various spending formulas depend on population. For example, if it’s known that the census won’t be adjusted, then I’d expect the government of New York City to put a lot of effort into convincing people to participate. If it is known that the census will be adjusted, then there’d be a lot less motivation for localities to do what it takes to boost participation.

Conditional on the data already being collected, you’d definitely want to make statistical adjustments; it’s a tougher call to decide on this ahead of time. Also, if you know for sure you won’t be adjusting, this will affect the effort you put into collecting the data in different places. So if you’re not going to adjust, you might as well make that decision right away.

To expand on this slightly, I think any debates over census adjustments are fundamentally political debates, not statistical disagreements. The scientific consensus on adjustment is pretty easy (although people can argue about the details of implementation, as noted by Lawrence in comments below). It’s the political consensus that’s difficult, as there are clear winners and losers. With a lack of political consensus, all you need is a little bit of dust and confusion in the air to give a sense of a lack of scientific consensus, which then gets piped back in to justify inaction in the political process.

P.S. Thanks to the commenters below for discussion of the legal aspect of this issue, of which I was unaware.


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