Making Sense of the Census: Why Sampling MightNot Be so Simple

Thomas RileyDavid Murray

Statistical Assessment Service

It was only 1997, but an apparently innocuous statistical dispute sud-denly turned the Year 2000 Census into a political hot potato. What is theproblem? And why are critics arguing that the proposed solution may beworse than the flawed system we already have?

THE PROBLEM

No statistics collected by the government are as important as thosefrom the Census. From apportioning Congressional districts to directing theflow of federal funds, the Census data undergird the nation's political struc-ture. It is critical, therefore, that the Census count be as accurate as possi-ble.

And yet we know that the Census is not accurate. Despite the enor-mous effort mounted every ten years by the Bureau of the Census, whichincludes mail-in forms sent to every household in the nation followed upwith door-to-door data collecting, the Census still does not provide an ex-act statistical portrait of America. It is widely believed that the Census "un-dercounts" us; it would be more accurate to say that the Census miscountsus. Supplemental research following the 1990 Census indicates that tenmillion people were left uncounted, while six million people were counted

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Please address correspondence to Thomas Riley, Senior Analyst, or David Murray, Direc-tor of Research, at STATS, 2100 L Street, N.W., Suite 300, Washington, D.C. 20037-1525.

Population and Environment: A Journal of Interdisciplinary StudiesVolume 19, Number 3, January 1998 1998 Human Sciences Press, Inc.

POPULATION AND ENVIRONMENT

twice. This means that approximately four million people, or 1.6% of thepopulation, remained uncounted. That may not sound like much in a na-tion of over 265 million, but when presidential and congressional electionscan hinge on the shifting of just a few thousand well-placed voters, thosefour million loom very large indeed.

WHO IS UNDERCOUNTED?

No single demographic characteristic links the undercounted. Theyinclude people who fail to mail in their forms (and are not home whenCensus-takers come knocking), migrant workers, fugitives from the law,people living in dangerous-looking housing projects that Census-takersmay have avoided, the homeless, illegal aliens, legal aliens who may besuspicious of government authority figures, and people who, for whateverreason, simply do not want to be counted.

There is some consensus, though, that minorities and immigrants areespecially likely to be undercounted. According to the Los Angeles Times,the 1990 supplemental sample indicated an undercount of 2.3% for Asian-Americans and Pacific Islanders, 4.4% for African Americans, 4.5% forNative Americans, and 5% for Hispanics, while the undercount for whiteswas 0.7%.

Although Robert Rosenblatt of the Times got these numbers right, it isimportant to pay attention to what, exactly, is meant by "undercounting."In an editorial against the use of statistical sampling in the Census, TheDetroit News perpetuates the mistake made by many in this dispute:namely, that the undercounted population is entirely composed of "minor-ity groups, undocumented aliens, and city dwellers." The percentageslisted above are statistical projections meant to be added to actually coun-ted populations. In other words, if these data are accurate, an actual headcount would find the Asian population to be 2.3% higher, the AfricanAmerican population 4.4% higher, etc. Even a 0.7% increase in the whitepopulation, however, represents approximately one million uncountedwhites. In addition to the more well-known urban undercount, there is asignificant rural undercount. Ironically, the very rich as well as the verypoor often go uncounted. Such is the price one pays for being off skiing inGstaad or at the winter place in Florida when the Census-taker comesknocking at your gated community. Ultimately, the controversy here turnsless over the exact racial proportions of the undercounted than over wherethey are located.

And herein lies the political interest. As far as the absolute number of

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congressional districts is concerned, it is a zero sum game: One state's lossis another's gain in federal funding and congressional districts. Sun Beltstates want as many of their burgeoning population as possible to be coun-ted, while Rust Belt states do not want their influence in Washington re-duced any further.

The Census count also affects how congressional districts are appor-tioned within each state. Imagine two bordering congressional districts,one urban and predominately black, the other suburban and predom-inately white. A third district is to be added that encompasses elements ofboth. How that line is drawn "creates" political majorities that stay in placefor a decade. This has been the grist for innumerable court cases and politi-cal fights over redistricting, the ammunition for which has always been theactual census countuntil now.

THE SOLUTION

How then to account for the uncounted? The Census Bureau proposesto actually count only 90% of the population and then apply a statisticalprojection that will ostensibly capture the remaining 10%. By creating astatistical sample of those who are most likely to be undercounted andthen factoring that back into the general total, the Bureau hopes arrive at amore accurate result. This approach has been used in varying forms bytest-marketers and pollsters for years, but at the Census level it raises somesignificant questions.

PROBLEMS WITH SAMPLING

First, the method proposed by the Census Bureau does not simply addthe statistical sample to the 90% actually counted. It takes the sample andprojects it back into the counted population, eliminating any distinctionbetween those who are physically counted and those who are "counted"by computer. In the event of error or change to the sample parameters, itwould be extremely difficult to disentangle those statistics at a later date.

Second, decreasing the number of Americans actually counted maydiminish both statistical confidence and public confidence in the Censusresults.

Indeed, test sample results have already shown troubling margins oferror. At the basic Census block level, standard error levels of plus or mi-nus 23 have been found at the 90% confidence level. That is, an unvisited

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block of apartments included in the Census as housing 100 residents couldhave as few as 77 or as many as 123 residents. When we move up to the95% confidence level (the "gold standard" for researchers) the error levelreaches plus or minus 28. (See Figure 1.)

These error levels diminish somewhat when using higher populationsample sizes, but statistician Clark Bensen (1997) has noted that "theatomic level of the census block is the building block for every district. It isthe starting place. If the reliability of the population counts at this lowestlevel is not extremely high, the results for every other level of census andpolitical geography will be suspect."

The Census Bureau recognizes that it may be substituting one form oferror for another. Its own in-house documentation acknowledges that whilethe proposed sampling methodology may help reduce " 'non-sampling er-ror' " (i.e, undercounting), " 'there will now be some measurable samplingerror associated with population totals'" (emphasis added) (Bensen, 1997).It is also far from clear whether the Supreme Court will allow a "sampledCensus" to stand. The Constitution dictates an "enumeration," and theCourt has not yet ruled on whether a projected statistical sample satisfiesthis definition.

Finally, once the sampling precedent is set, what is to prevent us, inprinciple, from lowering the actual enumeration from 90% to 80% or 70%or lower? Such tinkering with the data to arrive at what the population"should" look like seems likely to engender more, not less frustration over"not being counted." This also creates a powerful political temptation forthe party in power to skew the sample adjustment its way. The ability to"create" or "eliminate" millions of strategically-placed citizens with thestroke of a pen introduces a potent and disturbing new political weapon.

Our current Census methods do an insufficient job of cataloguing whowe are. Statistical sampling may help address this problem, but it also in-troduces a new set of errorsand a dangerous new set of political tempta-tions.

REFERENCE

Bensen, Clark (May, 1997). Confidence in population esdtimates from sampling. PoliticalData Analysis (web site: www.polidata.com) Lake Ridge, Va 22192.

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