Census and Sensibility

by Howard Fienberg
August 12, 2002

This spring, the U.S. Census Bureau announced plans to effectively replace the "long form" of the Census with the annual (and relatively new) American Communities Survey (ACS). Despite the potentially serious ramifications, the debate about this policy has not exactly been front-page news. When the Washington Post examined the debate on April 8, it remarked, "Most in the statistical community support the concept, although some have concerns." Yet nowhere in the article could be found what such concerns might be.


You don't have to be a technocrat to care. The numbers from the Census Bureau guide funding and effort across government at all levels. They tell us where new schools should be built to accommodate an influx of children and where new roads and mass transit systems should be added to deal with dreadful commutes. They also drive the wrenching political disputes over apportioning legislative districts and seats.


During the decennial census, every American household is supposed to receive a short form questionnaire, asking basic questions like how many people live in their domicile. One in six also gets a long form of 53 questions, which go into much greater demographic depth and detail (like income, housing, language, etc). The Bureau proposes to replace the long form with the ACS, an annual survey in pilot-testing since 1996 which covers ground similar to the long form, querying about 3 million people.


There are pluses and minuses to supplanting the long form with the ACS. On the plus side:


  • It would give the Bureau a permanent professional apparatus dedicated to running the ACS, which would make running the decennial census and training the decennial census-takers much easier and cheaper. The Bureau estimates that the long form accounts for about sixty percent of its work. Science magazine reported that in 2000, the Bureau spent about a million dollars to train temporary workers for follow-up interviewing with households that received the long form but did not respond. By contrast, the ACS would have several thousand dedicated staff, well-versed in survey-taking.


  • It would require the Bureau to compile a permanent master address file. Instead of creating one from scratch every ten years, a very time-consuming and costly production, this constantly updated file would make the decennial census much more accurate and save a fair bit of money over time.


  • It would yield more timely data. Not only could data be collected annually instead of every ten years, new and timely questions could be added to the questionnaire for faster results.


  • Since the ACS has a significantly smaller sample, is run over the telephone and is conducted by professionals, response rates are dramatically better than for the Census long form. While the ACS manages only 52 percent response on the initial run, dedicated follow-up attempts have raised the response rate as high as 96 percent.


However, on the con side:


  • The ACS enterprise is expensive. Officials expect to need about $124 million for the ACS in fiscal year 2003, and even more the year after. In the long run, the ACS might save money. But the long form, at the moment, is a bargain - getting this extra info at every decennial Census, aside from the hassles in follow-up interviews, costs very little.


  • The ACS is more timely, and reasonably rapid response questions can be added to the questionnaire, but the Bureau doesn't do "rapid" very well. Its forays into experimental questions have achieved mixed results.


  • At base, the smaller sample of the ACS translates to a larger margin of error. Off the record, some statisticians are concerned that the Bureau has not adequately tested the accuracy of the ACS sampling mechanism.


  • The ACS might end up missing the same people claimed to be missed even in the huge effort of the decennial survey. A test of the ACS method showed that response rates differ dramatically by race. While whites answered about 60 percent of the mailed surveys, blacks and Latinos answered only about 35 percent. The Bureau does follow-up interviews, of course, but only does in-person follow-up for 1 of every 3 households that do not return calls or cannot be reached by phone.


  • The larger question with the ACS is what to do with the data. While the Census data gets specific about regions, states, counties, cities, even street blocks, the ACS is a national sample. Because of the national sampling method, specific local data can not be inferred from the ACS. Statisticians have yet to decide how to solve this "statistical inference" problem. Any attempt to influence legislative apportionment using ACS data could prompt a political fight greater than any previous battle over statistical sampling in the Census.


Most data-hungry people, whether in government or business, are eager to give the ACS a try. They desperately crave data that is not two to three years out-of-date by the time it reaches them. But once the long-form goes the way of the do-do, it probably can't be resurrected. This major change in how we collect official statistics ought to inspire at least a little more debate before any final decisions are made.

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