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Reengineering the 2010 Census: Risks and Challenges (2004)

Chapter:4 American Community Survey

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Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

CHAPTER 4
American Community Survey

THE CONSTITUTIONAL MANDATE for the decennial census is to provide a basic head count for purposes of apportionment, but the nation’s need for accurate measures of its civic health has led the census to develop well beyond a simple count tabulated by age, race, and sex. Over time, the roster of questions included in the census expanded to cover a wide array of socioeconomic and demographic characteristics. The emergence of the statistical theory of survey sampling in the early 20th century brought with it the potential to collect detailed characteristics information without unduly burdening the entire American public. Asking detailed characteristics information from only a sample of the populace began in the 1940 census, when six questions on socioeconomic status were asked of only 5 percent of respondents. In 1960, the concept took its next evolutionary step when two separate census forms began to be used, a design feature that continued through the 2000 census. The short form covers the basic information items to be asked of all residents; the long form—administered only to a sample of the public—includes the complete battery of characteristics questions. In 2000, for example, the short form contained queries for six basic items—age, sex, Hispanic origin, race, relationship

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

to census respondent, and housing tenure (renter/owner), while the long form administered to roughly one-sixth of households added about 62 items, 36 of them pertinent to demographic and economic characteristics and 26 related to housing.

Fifty years after the development of separate short and long forms in the census, the Census Bureau proposes to make another change in the collection of population characteristics data by introducing the American Community Survey (ACS). A major household survey intended to include 250,000 housing units each month, the ACS would replace the decennial census long-form sample and permit continuous measurement of the same data items currently collected only every 10 years on the census long form. The 2010 census would therefore include only the short form, which would enable easier (and potentially more accurate) data collection in the census and save costs on data capture from completed paper questionnaires. At the same time, the data on characteristics currently collected on the census long form would be produced on a more timely basis, offering annual assessments rather than a static once-a-decade snapshot.

The potential rewards of the ACS are great, but so too are its inherent risks. The survey’s success is contingent on sustained long-term funding, and year-to-year fluctuations in allocated spending levels could cause severe data quality problems, particularly for small population groups. Estimation based on continuous measurement such as the ACS—most likely making use of moving averages of several years of data—also raises conceptual and feasibility issues that must be addressed in order for the survey to win support. These risks, and others, are significant, but perhaps the most important risk associated with the ACS is simply one of timing. A final decision on the methodology for the 2000 census was reached dangerously close to Census Day; extended delay in reaching agreement at all levels—the Census Bureau, the administration, and Congress—about the role of the ACS could similarly raise the risk of having to revamp census design very late in the cycle. The decision on whether the ACS will proceed in full—and, with it, determination of the fate of the census long form—is the single most important element in terms of defining the general shape, structure, and design of the 2010 census.

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

In this chapter, we discuss the background of the ACS and describe the current plans for a fully operating ACS in Section 4-A. We then begin our assessment by identifying key questions (4–B); these major questions generally center around the challenges of estimation using the ACS (4–C) and the basic quality of ACS data (4–D). Our general summary and assessment of the ACS’ proposed role in the 2010 census (4–E) is followed by an outline of major features required in the intensive research and evaluation effort that should complement ACS operations (4–F).

4–A BACKGROUND AND CURRENT PLANS

Work on what is now known as the American Community Survey commenced after Alexander (1993) revisited the idea of a continuous measurement survey for gathering long-form data as a complement to a short-form-only census (for historical context, see also Hauser, 1942; Kish, 1981, 1990). Two previous National Research Council panels supported the general principle of a continuous measurement survey and urged further research (National Research Council, 1994, 1995); however, National Research Council (1995) concluded that a proposal to implement the survey to replace the census long form in the 2000 census was infeasible, given inadequate lead time and unresolved conceptual problems. The ACS was also the focus of a 1998 National Research Council workshop to discuss research priorities (National Research Council, 2001b).

4–A.1 Test Sites and the Census 2000 Supplementary Survey

Though the ACS was ruled out as a replacement for the long form in 2000, the mid-1990s burst of research and writing about the prospects of continuous measurement launched a wider research and evaluation effort. Pilot data collection for the ACS began in four test sites in 1996. By 1999, data collection in this demonstration phase had grown to include thirty-one sites across thirty-six counties (U.S. Census Bureau, 2003c). During the initial pilot phase in 1996–1998, residents were sampled at a markedly higher rate—15 percent, increased to 30 percent in some communities—than is planned for the full-scale ACS.

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

More significantly, as the ACS began to be adopted as part of the developing 2010 census plan, an experiment was developed in conjunction with the 2000 census to attempt to address the basic question of operational feasibility (that is, whether it is possible for the Census Bureau to conduct the decennial census and an ongoing survey containing usual long-form items at the same time, both operationally and in terms of burden on respondents). Accordingly, the Census 2000 Supplementary Survey (C2SS) began in January 2000 and continued data collection through December 2000. This prototype ACS sampled from 1,203 counties and covered approximately 700,000 households over the course of the year. Data collection continued at these levels in 2001–2003. A report prepared as part of the 2000 census evaluation program concluded that operating a large continuous measurement survey in parallel with the decennial census was operationally feasible, based on the 2000 census and C2SS experience (Griffin and Obenski, 2001).

Original plans called for the ACS to begin full field implementation in 2003, a schedule that would support publication of small-area estimates in 2008. However, congressional stalemate on the budget for fiscal year 2003 delayed full implementation by at least one year.

4–A.2 Current ACS Implementation Plans

Under the funding levels appropriated for fiscal 2004, questionnaire mailing for a full-scale ACS would begin during the fourth quarter (July–September) of fiscal 2004. Follow-up field work would be deferred until after September 2004, pushing the considerable expense of field interviewing into the fiscal 2005 budget process. Prior to the fourth quarter mailing, data would continue to be collected in the thirty-one test sites and at the C2SS levels (Lowenthal, 2003a).

When the ACS is fully fielded, it will use as its sampling frame the same Master Address File (MAF) used by the decennial census. The annual sample of housing units chosen for participation in the survey will be divided into monthly mailout panels, each of which will be a systematic sample across the complete address list. Thus, it is intended that each month’s sample will be a rep-

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

resentative sample (approximately ) of the population of each area of the United States. In practice, this simplified sample selection process will be modified by practices similar to those used for the decennial census long form, including oversampling of small geographic areas.

The ACS is intended to be administered primarily via mailout/ mailback. However, the proposed ACS techniques to follow up with households that do not return the mail form differ from decennial census practice. All mail nonrespondents will be initially followed up by computer-assisted telephone interviewing (CATI) during the month following questionnaire mailout, if there is an available phone number. After CATI follow-up, a random one-third of the remaining nonrespondents will be designated for follow-up by field enumerators using computer-assisted personal interviewing (CAPI). The precise nature of this sequential follow-up process remains to be determined; there are tentative plans to sample areas with low mail and telephone response rates at a higher fraction rather than a strict one-third random sample.1 This oversampling may help to make sample variances more comparable across areas.

The stagewise nature of ACS follow-up leads to another important design feature, which is that all of the information collected in a given month will be used as inputs for that month’s estimates. That is, a particular month’s estimates may include mailback responses from the present month’s systematic sample of housing units as well as completed telephone and personal interviews from one and two months prior, respectively. This design choice is advantageous in that it simplifies data processing and production load—there is no need to wait until month t+2 for final resolution of all the housing units chosen in month t before processing responses already submitted. But it does raise complex methodological challenges, including the choice of weighting methods to address unit nonresponse.

While the size of this survey will make possible some direct small-area estimates, the estimates for areas with a population

1  

Due to budget constraints, the Bureau may be required to reduce the sampling rate in higher mail and telephone response areas to accommodate this oversampling. The implications of such a shift need to be researched ahead of time before plans are finalized.

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

of less than 65,000 typically will be produced by aggregating information over either 3 or 5 years, depending on the size of the area. At this time, moving averages are planned to be used for these aggregate-year estimates, though other possibilities could be considered in the future.

The need for a 5-year window to produce detailed small-area estimates puts a firm constraint on the date of full ACS deployment. The initial plans for full deployment in 2003 would have produced small-area estimates in 2008, allowing some time for the new ACS figures to gain acceptance as a long-form replacement. To match the long-form data production schedule of the 2000 census, the absolute deadline for full (and sustained) implementation of the ACS is 2007, which would permit the publishing in 2012 of national estimates analogous to those from the long form.

4–B ASSESSING THE ACS

In simplest terms, the root practical question that must be answered in justifying the ACS is whether the information generated by the survey is an adequate replacement for the data currently collected on the census long form. Parsed at the most basic and literal level—whether the ACS and the long form are substitutable in content—the answer is simple. By design, the ACS covers the same topics and data items as the census long form; exact question wording and ordering may vary, but in general terms the content matches. Thus, in the simple sense of topical content, the ACS is an obvious substitute for the long form.

The more challenging question is whether the ACS can replace the census long-form sample in terms of performance and function. This basic question can be further subdivided into key subquestions, the answers to which are vital to bolstering the case for the ACS.

  • For all but the largest population or geographic groups, ACS estimates will be based on averages across multiple years of data. Is the ACS able to satisfy all of the needs currently addressed by long-form data, or are there applications based on the census long form for which substitution

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

of a moving average-type estimate from the ACS would be inappropriate?

  • How well will ACS estimates match other estimates of the same phenomena? That is, how will ACS measures compare in level or trend to traditional long-form estimates or to other survey measures?

  • What is the quality of ACS estimates and data relative to the census long form? Specifically, what can be said about error—both bias and variance—and undercoverage in data collected through the ACS, and how do they compare with those incurred through the census long form?

These and other questions involve concerns about methods of estimation based on the ACS and about the inherent quality of ACS data and estimates; we offer more detailed comment on these concerns in the following two sections.

4–C ESTIMATION USING THE ACS

4–C.1 Adequacy of Moving Averages as Point Estimates

A basic concern about the American Community Survey as a replacement for the census long form is whether ACS estimates—which, particularly for small areas or groups, would be moving averages of multiple years’ data points—can effectively replace fixed-point-in-time estimates. Specifically, the concern is whether fund allocation formulas or other public and private planning needs for demographic data can be addressed using a combination of data from multiple years. The Census Bureau has issued a draft report that attempts to address users’ concerns about this shift (Alexander, 2002), and Zaslavsky and Schirm (1998, 2002) outline the advantages and disadvantages a locality may experience through use of either a moving average or a direct (census) estimate.

The crux of the debate on this point is that a moving average is a smoothed estimate; by averaging a particular data observation with other observations within a particular time window, the resulting estimate is meant to follow the general trend of the series but not be as extreme as any of the individual points. The

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

ramifications of this method emerge when moving average estimates are used in sensitive allocation formulas or compared against strict eligibility cutoffs. A smoothed estimate may mask or smooth over an individual-year drop in level of need, thus keeping the locality eligible for benefits; conversely, it may also mask individual-year spikes in need and thus disqualify an area from benefits. It is clear that the use of smoothed estimates is neither uniformly advantageous nor disadvantageous to a locality; what is not clear is how often major discrepancies may occur in practice.

One answer to this conundrum is to use sample-based estimates from individual years instead of moving averages. These estimates would be unbiased in terms of probability but could be highly variable, which would affect aspects of formula grants such as “hold-harmless” provisions.2 A related worry that has been expressed about moving averages is that, by incorporating estimates from other time periods, the estimates for a given period could be substantially biased and not truly reflect the conditions for that period. The empirical challenge is to assess the bias that may result from averaging over 3 years of data compared to 5, and try to weigh the magnitude of that bias against the bias associated with using an up-to-12-years-old long-form estimate. Intuitively, it is sensible that, when examining data series in which change is substantial between decennial census years, moving average estimates would be preferable to seriously out-dated estimates. When there is little change through the decade, there should be little difference between the two estimates. However, since this is an empirical question, the Census Bureau should carry out research that helps to evaluate this trade-off.

The continuous measurement properties of the ACS give it unique advantages over the decennial snapshots available from the census long form, but they also raise another, related point of

2  

A “hold-harmless” provision in a funding formula is one that limits the amount by which an allocation can change from one year to another; for instance, under a 70 percent hold-harmless level, a unit’s allocation may only decrease by up to 30 percent. In a hold-harmless situation, an unusually volatile observation one year due to increased variability could mean that the unit’s allocation may remain out of true alignment for several cycles due to the amount of allocation automatically carried over.

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

concern regarding moving averages: assessment of year-to-year change in a data series. It is incorrect to use annual estimates based on moving averages over several years when assessing change since some of the data are from overlapping time periods and thus identical. At the least, the results will yield incorrect estimates of the variance of the estimates of change. Therefore, users should be cautioned about this aspect of the use of moving averages. Along the same lines, moving averages present the same types of problems when they are used as dependent variables in various statistical models, in particular time-series models, and in some regression models. Therefore, the Census Bureau could bolster the case for the ACS and potentially help relieve users’ concerns if it produced a user’s guide that details the statistical uses for which moving averages are and are not intended, the problems they pose to users, and the means to overcome them.

4–C.2 Comparing ACS/C2SS to the Census Long Form

Thus far, we have outlined from conceptual and theoretical perspectives the issues surrounding the adequacy of ACS estimates to replace the long form. It is also natural to address the question from a more pragmatic point of view: the ACS and the census long form purport to measure the same basic phenomena, but do the resulting data from both series actually tell the same story?

Comparisons of how the ACS or C2SS estimates match census long-form estimates implicitly treat the census long-form data as an effective “gold standard”—a questionable assumption at best, given that it discounts the various (and sometimes substantial) sources of error to which the long form is subject. First, the long-form data for small areas are subject to substantial sampling error. In addition, as mentioned above, the long form is particularly subject to nonresponse, and for some sample items the amount of nonresponse for the long form in the 2000 census was extremely high (National Research Council, 2001a, 2004).

Love (2002) has identified a number of sources of differences between the ACS (or C2SS) and long-form census estimates that complicate any direct comparison. These include differences

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

in: reference dates; modes of nonresponse follow-up; criteria used to decide if a response is acceptable; edit and imputation techniques; methods for data capture and processing; the use of proxy interviews (they are accepted for the decennial census but not by ACS); definition of respondent eligibility; and weighting procedures used to address nonresponse and sampling (e.g., the weighting of the long-form estimates to the basic complete-count data). The reference period associated with a question item is of particular interest for ACS estimates, since annual averages will be the average of responses corresponding to twelve different reference periods, depending on when the questionnaire was applied. There are also differences in the target population; for example, the ACS does not currently include group quarters in its survey, but the census does.

Work on comparing the ACS (test sites) and C2SS estimates to census long-form estimates has been initiated by the Census Bureau. To date, what is known is that there are some substantial differences. Generally, these differences can be explained by the amount of sampling error in the two surveys (U.S. General Accounting Office, 2002a); however, examination of C2SS data suggests significant differences for the number of housing units lacking complete plumbing facilities and for the number of unpaid workers in a family, for instance. At the state level, a large number of C2SS estimates differed from the long-form estimates by at least 10 percent, including the number of workers that commute using public transportation, the number of households with income above $200,000, the number of housing units that lack complete plumbing facilities, and the number of renter-occupied units with gross monthly rent of $1,000 to $1,499.

The Census Bureau needs to complete this analysis, including the contribution of sampling variance, for all years of data collection, and attempt to identify the sources of differences other than sampling error. A priority of this analysis should be responses related to residency, but all responses should be examined.

4–D QUALITY OF ACS ESTIMATES

The error associated with ACS data may be decomposed into sampling error (sample variance) and nonsampling error, the

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

latter of which can be further separated into error due to nonresponse and measurement error due to various causes.

At the most basic level, sampling error in the ACS will be slightly larger than that for the long-form sample because the total ACS sample size over a 5-year period will be slightly smaller than that for the census long form. On its own, this difference is unlikely to have a substantial impact on users. However, sampling error due to initial mail and CATI nonresponse is widely variable and could be appreciable in some small areas.3 As a result, the Census Bureau is considering raising the sampling rate for CAPI follow-up for areas with high mail and telephone nonresponse to make this source of sampling error more comparable across areas.

It should be noted as we review these issues that, generally, these concerns are generic to all surveys, including the census long form—that is, the concerns are not raised as specific flaws of the ACS. They are, nonetheless, features of the ACS that must be measured and weighed in deciding how best to use the data.

4–D.1 Estimating Nonresponse
Unit Nonresponse

One part of nonresponse in a survey program like the ACS is unit nonresponse—that is, failure to obtain questionnaires and data from households selected for inclusion in the sample. A common combined measure of unit nonresponse and survey undercoverage is the sample completeness ratio, which is the sample-weighted estimate of the population count for a certain area divided by the census count for the area. The sample completeness ratio nationally for C2SS was 90.2 percent, while the comparable figure for the 1990 long-form sample was 89.7 percent (U.S. Census Bureau, 2002b). These figures may appear close, but some care must be taken in interpreting them. For example, the long form accepts proxy responses from landlords or neighbors while proxies are not permitted in the ACS or C2SS, and it is generally accepted that proxy responses are of lower

3  

See Salvo and Lobo (2002) for relevant discussion on this point.

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

quality than responses by household members.4 So the programs, and these ratios, are not directly comparable. Still, the C2SS seems to be roughly equivalent to the long form with respect to unit nonresponse and survey undercoverage.

Another statistic that is often examined to assess the quality of survey data collection is the rate of mail questionnaire return. This is because, in the census context, information collected through self-response is typically considered to be of higher quality than information collected through field enumeration (National Research Council, 1995). For the C2SS, the mail return rate was 51.9 percent (U.S. Census Bureau, 2002b:11), lower than the 71 percent for the 2000 census long form (National Research Council, 2004:100). For the 2000 ACS in the Bronx County test site, the mail return rate was 36.4, compared to 55.8 for the long form in the 1990 census (Salvo and Lobo, 2002). While this difference could contribute to a lowering of the quality of ACS information relative to census long-form information, it might be addressed by improved field data collection.5

Salvo et al. (2003) apply a metric of minimal completeness to specially prepared operational data from the 2000 ACS and the 2000 census for Bronx County, New York (one of the thirty-one test sites.6 They found that 49 percent of enumerator returns

4  

Nonresponse follow-up for census long-form data was often concluded with the collection of short-form data only (that is, a premium was placed on gathering the basic short-form characteristics from as many nonrespondents as possible rather than insisting on a complete long-form return). Such forms are treated as long-form unit nonresponse.

5  

As Salvo and Lobo (2002) demonstrate, there is substantial heterogeneity in the ACS mail return rate and in other measures of nonresponse as a function of characteristics often associated with being difficult to count in the census. Therefore, it should be understood that both the ACS and the census long form are more or less successful in collecting quality data depending on the area of interest.

6  

Salvo et al. (2003) use a measure of completeness similar to that used in census processing to determine if a household data record is complete enough to be considered “data-defined.” To be complete under this metric, at least one member of the household had to have answered two of the basic complete-count items asked on the census short form (e.g., age or sex) and two of the sample data items asked on the census long form. Preliminary results of the Salvo et al. (2003) analysis were reported in Salvo and Lobo (2002).

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

for the long form failed the completeness test, whereas only 14 percent failed for the ACS.

The overall weighted survey response rate for the ACS has been calculated as 95.4 percent, which is very high for a household survey. This rate includes responses across the different possible modes of administration (telephone, in-person) but does not factor in survey undercoverage.

Item Nonresponse and Invalid Response

Extant research based on item imputation rates for responding households not only measures item nonresponse but also includes imputations for responses that fail consistency edits. However, this complication is relatively infrequent and is consistently applied to both the C2SS and the census long form. As a result, we feel that it is reasonable to compare item imputation rates to measure the impact on data quality from item nonresponse. Item imputation rates for the C2SS were substantially lower than those for the 2000 census for the basic data items on both the short and long forms. For example, for age, the census imputation rate was 3.6 percent, whereas for the C2SS it was 2.4 percent. Salvo and Lobo (2002) report that the allocation rate (essentially the same as the item imputation rate) was typically much higher in the 1990 long form than in the 2000 ACS in Bronx County. Furthermore, this difference was strongly related to the lower quality of field data collection for census long-form information in comparison to the ACS. The U.S. General Accounting Office (2002a) reported on preliminary work carried out by the Census Bureau for long-form items in which the imputation rates were slightly higher than for the C2SS.

More complete work on comparing item imputation rates between the C2SS and the 2000 census long-form is reported in National Research Council (2004:Ch.7). Table 4-1 reproduces their analysis of comparative imputation rates for 15 person items and 12 housing items, by type of return. Imputation rates were lower for the C2SS than for the census long-form sample with one exception (year structure built). As National Research Council (2004:284–286) describe, C2SS enumerator (follow-up) returns required less imputations than mail returns for all person-item

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

Table 4-1 Imputation Rates for Selected Long-Form Items, 2000 Long-Form Sample and Census 2000 Supplemental Survey, by Type of Response, Household Population (weighted)

Item

2000 Long Form

Census 2000 Supplementary Survey

Total

Self

Enumerator

Total

Self

Enumerator

Person Items

 

Marital Status

2.2

1.4

4.3

1.8

2.4

1.0

Educational Attainment

7.2

5.2

12.0

4.8

4.9

4.7

English-Speaking Ability

7.6

7.3

7.9

6.0

10.5

2.3

Place of Birth

9.2

7.8

12.5

6.4

8.1

4.1

Residence 5 Years Ago

5.8

4.3

9.6

4.0

5.6

1.8

Physical Activity Disability

7.6

7.1

8.9

5.2

7.4

2.1

Work Disability

11.4

12.2

9.3

5.9

8.3

2.2

Veteran Status

7.5

6.1

11.0

4.7

6.1

2.5

Employment Status Recode

11.1

10.2

13.4

6.0

8.2

2.6

Place of Work - State

9.7

7.3

15.5

5.8

6.5

4.8

Transportation to Work

7.6

5.4

13.0

4.6

5.5

3.3

Occupation Last Year

14.9

13.2

19.2

9.5

11.1

7.1

Weeks Workeda

19.3

18.6

20.9

9.6

11.1

7.3

Wage and Salary Income

20.0

15.0

32.6

16.4

13.0

21.4

Income, All Sourcesa

 

100 Percent Imputed

24.5

18.9

38.5

20.0

16.1

25.7

Some Imputedb

29.7

25.5

40.3

23.9

20.7

28.6

Housing Items

 

Units in Structure

4.4

4.9

3.0

1.4

1.6

1.0

Year Structure Built

11.7

9.3

18.0

13.4

7.4

22.8

Number of Rooms

6.2

6.2

6.4

2.6

3.4

1.4

Complete Plumbing

3.4

3.5

3.1

1.0

1.4

0.3

Complete Kitchen

3.4

3.5

3.1

0.9

1.3

0.3

Fuel Used for Heating

7.4

6.3

10.1

2.1

1.6

2.8

Electric Costc

17.1

13.6

26.1

6.9

4.3

11.0

Monthly Rent

15.6

13.2

19.2

5.3

4.2

6.3

Property Taxes

32.0

27.0

49.6

20.8

13.7

35.4

Value of Property

13.3

12.3

16.6

9.7

6.0

17.4

NOTES: Rates (percents) exclude assignments. In 2000, self responses included mail, telephone, Internet, and Be Counted returns; enumerator responses included forms obtained in nonresponse follow-up, list/enumerate, and other field operations. In the C2SS, self responses included mail; enumerator responses included forms obtained in telephone and in-person follow-up.

a For 1999 in the 2000 census long-form sample; for last 12 months in the C2SS.

b Includes 100 percent of income imputed.

c Annual cost in the 2000 census long-form sample; last month’s cost in the C2SS.

SOURCE: National Research Council (2004:Table 7.5); tabulations by U.S. Census Bureau staff from the 2000 Sample Census Edited File (SCEF) and the Census 2000 Supplementary Survey edited file, provided to the Panel to Review the 2000 Census spring 2003.

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

characteristics except income, while 2000 census long-form sample self (mail) returns tended to be more complete than enumerator returns for the same characteristics. This suggests the effect of better training among the C2SS interviewers relative to the temporary census enumerators. It also suggests the effect of the priority in the census of collecting at least (and, if necessary, only) the basic complete-count items like age and gender, whereas the C2SS interviewers are more likely to press for responses to all questions. However, Table 4-1 suggests that this distinction does not apply to the housing data items; for those questions, enumerator returns require more item imputation than self returns for both the C2SS and census long-form sample.

4–D.2 Quality of Imputed Responses

Rates of unit and item nonresponse are only partially informative as measures of the error rate due to nonresponse. This is because the imputation and weighting routines that the Census Bureau uses to treat item and unit nonresponse (and survey undercoverage) can offset some of the information loss, depending on the extent to which the various assumptions used to support the imputation methods hold (e.g., responses missing at random). Therefore, measures of the quality of imputations are an important additional measure of the impact of item and unit nonresponse.

This impact could be measured either through a reinterview survey or through matching to a more reliable source of data (possibly administrative records or highly reliable household surveys). But both approaches are problematic. Reinterview surveys of appreciable sample size are expensive and require high-quality interviewing to elicit higher-quality responses than provided earlier. Matching studies are limited by the availability of higher-quality, comparable information—a difficult standard to meet. The Census Bureau is conducting a matching study comparing C2SS responses to those for the 2000 census short form, though errors in both systems complicate the comparison.7

7  

Due to the design of the C2SS—specifically, the provision that the same respondent would not receive both the census long form and the C2SS—this matching is feasible only for characteristics on the census short form.

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

Some interesting work has been done on responses to race and ethnicity questions (Bennett and Griffin, 2002). A less satisfying variant of this analysis could still be carried out for small geographic aggregates—for example, comparing census and ACS frequencies and means for responses at the tract level, which would overcome the inability to match individual long-form responses. Some of this work is being conducted by the Census Bureau and is discussed below. Historically, there were matching studies of census responses to Internal Revenue Service (IRS) and Current Population Survey (CPS) data for earlier censuses (Bureau of the Census, 1964, 1975b),8 and excellent reinterview studies were done in the 1970s and 1980s (Bureau of the Census, 1970, 1975a). Also, limited research on the quality of the imputations for 1990 was carried out by Thibaudeau (1998), but comparable work has not been done for 2000.

4–D.3 Measurement Error

Measurement error consists of differences between the response that was intended by the survey designers given a household’s characteristics and the response that was actually captured. Possible contributors to measurement error include: misunderstanding of a question by the respondent, collecting data for the wrong time period, responding in the wrong units, transposing digits, making errors in capturing the response, intentional lying by either the respondent or the field enumerator, and so on.

It is reasonable to assume that, generally, the measurement error in ACS will be either comparable to, or very possibly somewhat less than, that for the census long form. This assumption follows from ACS design specifications: the ACS interviewing staff will be more experienced than short-term census enumerators and will be forbidden to use proxy respondents.

8  

Confidentiality concerns in the 1980s and 1990s led the IRS to restrict access to data, even for statistical purposes, thus precluding further census matching studies in recent decades. More recently, the IRS has facilitated limited administrative records research by the Census Bureau using IRS data with appropriate safeguards.

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

One challenge in comparing measurement error between the ACS and the census long form is reconciling the different definitions of residence in the two systems.9 Both definitions are valid and defensible, and each may have particular advantages in different contexts, but their basic differences complicate comparison. Moreover, the ACS stages data collection over 3 months, and this may induce error due to temporary vacancies and frequent moving. For analytic purposes, the moving time window of the ACS may also present difficulties in interpreting quantities like income: each interview’s snapshot is intended to capture a respondent’s income for the 12 months preceding the interview, as opposed to the fixed prior calendar year reference frame of the census (1999, for income reporting in 2000), and this difference may complicate time-series comparisons.

4–E SUMMARY AND ASSESSMENT

4–E.1 Benefits and Costs

Arguably, the most compelling benefit of the ACS is the increased timeliness of its estimates relative to census long-form estimates: ACS data products are at most 3.5 years out of date when released while census long-form data products are never less than 2 to 2.5 years out of date and can be as much as 12.5 years out of date. Currently, using census data to develop lower bounds on the amount of year-to-year change for various estimates—for example, poverty rates—involves examining census-to-census differences and dividing by ten whereas this annual change can be measured directly under the ACS.

Operationally, relative to the decennial census, the prime advantage of a full-fledged ACS for the Census Bureau is the prospect of a short-form-only census. Though the census long

9  

The census attempts to capture “usual residence”—the location where respondents usually live or spend most of their time. By comparison, the ACS captures “current residence,” the place where respondents are at the time of the interview. More precisely, the ACS uses a “Two Month Rule”: any respondent at a sampled household unit who has been living at the location for more than two months is considered a current resident (U.S. Census Bureau, 2003c). This can create differences for migrant workers or “snowbird” retirees who live for lengthy periods in different areas of the country.

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

form is delivered to only a fraction of the population—in the 2000 census it was administered to approximately a 1-in-6 sample—the operational burden is tremendous. Completed long forms constitute a mountain of paper, and each form must be unstapled (running the risk of pages being mishandled) before processing. Moreover, the short form is inherently more manageable than the long form in terms of delivery options; though administration of a census long form via the Internet, a portable computing device, or telephone (interactive voice response) is no doubt possible, having to deal only with a short form makes implementation of these response technologies much simpler, not to mention more palatable to respondents.

A great strength of the ACS relative to other national household surveys is its large sample size, which allows it to provide small-area information about the American population, including population characteristics profiles for counties, cities, and other local areas. Over a 5-year period, the survey’s sample size will approximate that of the census long form, supporting the production of estimates for small and nonstandard geographical areas, such as school districts and traffic analysis zones. In addition—and again given the large sample size—information will be available for population groups defined by factors other than geography, including racial and ethnic groups, age classes, occupational groups, and educational and health categories. (Tabulations can also be prepared for subpopulations with some combination of these characteristics.)

While the census long form can only provide these small-area profiles in once-per-decade snapshots, the ACS collects information continuously throughout the decade. Therefore, the ACS has the important advantage of providing estimates of the intercensal dynamics of small-area changes in the many variables listed above. Such estimates, which have been almost nonexistent up to now, can provide important information for policy initiatives and public and private planning.

The ACS may eventually permit researchers to develop an integrated framework for more accurate small-area estimation, perhaps combining one or more waves of ACS data with results from administrative records, other household surveys, and the short-form decennial census. This broader framework would

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

incorporate the ACS as a supplement to the social and demographic information currently collected by existing surveys and administrative records systems. There are a variety of synergies that can be imagined between the ACS and household surveys such as the Current Population Survey, each drawing on the other to improve the information collected.

As we commented in detail in Section 4-D, much work must be done to clarify the quality and accuracy of ACS estimates from a statistical standpoint. That said, there are also reasonable arguments from the perspective of survey methodology that the ACS may provide more accurate information than the census long form. During ACS nonresponse follow-up operations, ACS data would be collected by interviewers with substantially more experience—having done the work continuously—than the temporary enumerators employed during the census. Moreover, by spreading the demand on respondents to provide detailed personal and household information over the decade, the ACS may also be less susceptible to flaws and inaccuracies that may arise from nonresponse in a once-a-decade measurement. During the 2000 census, concern over the perceived intrusiveness of the long-form questions was well publicized, leading to the conjecture—albeit one that has not been empirically documented—that this concern may have negatively affected response rates on long-form questions and, accordingly, impaired the accuracy of long-form data.

These benefits—particularly the key benefit of increased timeliness—must be weighed against the costs of the ACS. Given that it cannot “piggyback” on some of the infrastructure provided by the decennial census, one might assume that the ACS could cost more than the marginal cost of the long form it is replacing. However, the Census Bureau has argued that operational efficiencies will make a short-form-only census complemented by the ACS a less expensive option than a mixed long-and-short-form traditional census. In congressional testimony on May 13, 2003, Census Bureau director C. Louis Kincannon commented that “our current estimates indicate that three components of the 2010 Census [the ACS, the MAF/TIGER Enhancements Program, and early planning and testing] will cost approximately $11.2 billion. However, if we change course right now and re-

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

vert to a traditional census, the cost will increase to more than $12 billion and perhaps much more.”10

In its original presentation of its 2010 census strategy, the Census Bureau argued that most of the additional costs of the ACS can be paid for through the associated efficiency gains in the 2010 census. According to the Bureau, these savings would result by eliminating the collection and processing of long-form information during the decennial census, through improvement of MAF/TIGER, and through use of hand-held data collection devices to facilitate field follow-up of mail nonrespondents. As the panel noted in its letter report (National Research Council, 2001c), we have not seen validation of this claim based on empirical evidence and suggest that a fuller cost-benefit analysis of the ACS would help bolster the case for the survey.

In 1995, a previous Committee on National Statistics panel studying the decennial census offered its comments on an idea “which the Census Bureau has recently been investigating”:

to drop the long form from the census and substitute a continuous measurement survey—that is, a large monthly survey of perhaps 200,000 to 500,000 households. By averaging the results of the monthly surveys over a period of 3 to 5 years, more timely long-form-type data, accurate enough for use in relatively small geographic areas, could be produced….

In its preliminary work, the Census Bureau has speculated that the costs of the new continuous measurement survey over a decade could be roughly offset by the cost savings from dropping the long form from the census and by other cost reductions that might be achieved in intercensal operations….

Although we believe that the proposed continuous measurement system deserves serious evaluation, we conclude that much work remains to develop credible estimates of its net costs and to answer many other fundamental questions about data quality, the use of small-area estimates based on cumulated data, how continuous measurement could be integrated with existing household surveys, and its advantages compared with other means of providing more

10  

The remarks are quoted from the director’s prepared testimony before the U.S. House Subcommittee on Technology, Information Policy, Intergovernmental Relations, and the Census at a hearing on the ACS’ potential to replace the census long form in 2010.

 

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

frequent small-area estimates. In our judgment, it will not be possible to complete this work in time to consider the use of continuous measurement in place of the long form for the 2000 census (National Research Council, 1995:9).

Nearly a decade later, faced with the task of offering advice on making the vision of continuous measurement a reality in time for the 2010 census, the similarity between the arguments then and now is uncanny. Similar, too, are the points of concern; the current panel is hard-pressed to improve upon the basic summary of concerns outlined by our predecessors. We are, however, much more sanguine that a compelling case can be made for the ACS and that it is a viable long-form replacement in the 2010 census.

In summary, the panel appreciates the enormous potential benefit of the ACS—of having a program for continuous measurement of key social and demographic variables of national interest. The ACS presents a unique source of timely information that could be extremely useful to public and private planning and that could be used to support more effective and targeted fund allocation. The potential benefits of the ACS are self-evident and require little salesmanship. However, what does require fuller justification is how these benefits offset the costs of the program and, more fundamentally, how the program works as a true long-form replacement. The panel is optimistic that such a compelling case can be made, though it will take continued evaluation work and research.

Recommendation 4.1: The Census Bureau should continue research to understand the differences between and relative quality of ACS estimates and long-form estimates, with particular attention to measurement differences and error from nonresponse and imputation. The Bureau must work on ways to effectively communicate and articulate those findings to interested stakeholders, particularly potential end users of the data.

The fact that the Census Bureau has not done more in comparing the data collected from the thirty-one ACS test sites, the

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

C2SS, and the 2001 and 2002 Supplementary Surveys with the data collected by the 2000 census long form is disappointing.11 Such analyses could be used to assess the quality of ACS data and would be helpful in making the argument for transition from the long form to the ACS. This deficiency is probably due to limited analytic resources at the Census Bureau and creates an argument for “farming out” this analysis to outside researchers. Furthermore, since access to local information is very useful in interpreting the results, the Census Bureau should explore whether local experts might be interested in assisting in this effort.

Recommendation 4.2: The Census Bureau must make ACS data available (protecting confidentiality) to analysts in the 31 ACS test sites to facilitate the comparison of ACS and census long-form estimates as a means of assessing the quality of ACS data as a replacement for census long-form data. Again, with appropriate safeguards, the Census Bureau should release ACS data to the broader research community for evaluation purposes.

Recommendation 4.3: The Census Bureau must issue a guide for users of ACS data that details the statistical implications of the difference between point-in-time and moving average estimates for various uses.

Part of a fuller justification of the ACS necessarily involves a cost-benefit assessment: enumeration of all benefits and costs, measurement or postulation of the benefits and costs, and comparison with costs and benefits (including data collection and processing) of the current approach (the census long form). The panel acknowledges that it is difficult to put a price tag on the value of more timely data, but coming to terms with cost-benefit

11  

As this report went into production, the Census Bureau released additional information on ACS quality metrics on their Web site at http://www.census.gov/acs/www/UseData/sse/index.htm [3/1/04]. In addition, the Bureau has commissioned some studies comparing 1999–2001 ACS and 2000 census long-form-sample data for several ACS test sites; those are expected to be released later in 2004.

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

trade-offs is an important part of assessing the program. Realistic assessment of the costs and benefits is complicated by the fact that so much remains to be demonstrated regarding the relative accuracy of ACS estimates and their applicability in the host of applications that currently use long-form data. We are optimistic that increased Census Bureau attention to informing data users and stakeholders (whether established users of the long-form data or newcomers) about the unique features and challenges of working with ACS data will build a stronger case for the survey.

4–E.2 ACS Funding

Given our panel’s charge, the most basic question we face is whether the ACS is a satisfactory replacement for the census long form (and therefore something that should be the foundation of 2010 census planning as it has become). We recognize that significant estimation and weighting challenges must be addressed; the survey’s costs, benefits, and uses must also be clearly articulated in order to convince users and stakeholders of its effectiveness. However, we do not see any looming flaw so large in magnitude that full ACS implementation should be set aside.

We therefore encourage full congressional funding of the ACS and are heartened that funds for launch of the full-scale ACS in late fiscal 2004 have been approved. Moreover, the administration’s fiscal 2005 budget request covers a first full year of funding for the ACS. We emphasize that it is important for the continued role of the ACS in 2010 to be decided early, within the next 2 years. Implementation of the ACS would allow the 2010 census to consist only of the short-form questionnaire, a design feature that is too critical and too wide-reaching to leave unresolved until late in the decade. The short-form-only census would facilitate broader Internet data collection and the use of PCDs to collect respondent data; it would also reduce the data collection effort and simplify use of multilanguage forms. But a late reemergence of the need for long-form data collection would remove any efficiencies the Census Bureau had developed from its streamlined design.

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

Recommendation 4.4: As soon as possible, based on the 2006 proof-of-concept test, the Census Bureau should work with Congress and the administration to secure agreement on the overall design for the 2010 census and the American Community Survey (ACS). Extended delay in finalizing an overall design for the 2010 census—such as occurred in the preparation for the 2000 census—would unacceptably heighten the risk associated with the 2010 census. The role of the ACS is of particular concern; failure to secure commitment to the ACS as a replacement for the census long form would severely impair plans for a short-form-only census and undercut the ability to provide reliable small-area characteristics data by 2010.

The Census Bureau should identify the costs and benefits of various approaches to collecting characteristics information if support for the full ACS is not forthcoming. These costs and benefits should be presented for review so that decisions on the ACS and its alternatives can be fully informed.

Funding for the ACS is, of course, not a decision of the Census Bureau but of Congress. The panel is encouraged by statements in a recent hearing on the ACS that indicate that congressional authorizers are aware of the importance of making a clear and early decision about ACS funding. Specifically, at a May 13, 2003, hearing on the ACS, Representative Adam Putnam (R-FL), the chairman of the House Subcommittee on Technology, Information Policy, Intergovernmental Relations, and the Census, commented in his opening statement:

I am also very aware that we are rapidly approaching the point where the Census Bureau needs to know one way or the other if there will be a long form in the 2010 census or will the ACS be the new survey tool. It’s fundamental to a successful 2010 Census that we let the Census Bureau know as soon as possible how the Congress expects the Census to be conducted. I’m hopeful that we can continue to work together to resolve these final remaining issues, and that Congress can make a final determination on full funding for the ACS in the near future.

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

It is essential, however, that Congress recognize that funding of the ACS is a long-term commitment. The benefits of the ACS will be jeopardized if the survey program is faced with oscillating budget commitments. Cuts in funding (and with them reductions in sample size) will impair the overall quality of the survey, with the most pronounced impact on the ability to produce estimates for small geographic areas and population groups. We strongly encourage the Census Bureau to conduct research that quantifies the sensitivity of ACS-based estimates to fluctuations in sample size, in order to make the case for sustained ACS funding more compelling to policy makers.

4–E.3 Contingency Planning

We endorse the ACS and strongly recommend that it replace the long form in the 2010 census. That said, we must reiterate our recommendation from previous reports that the Census Bureau begin contingency planning to be prepared should support for the ACS not be forthcoming. In our letter report (National Research Council, 2001c), we strongly urged the Census Bureau to make contingency planning a focus of its planning efforts, with particular attention to the funding levels for the ACS. The difficulty of securing fiscal 2003 funding for the full launch of the ACS underscored the importance of that recommendation. The obvious fallback contingency plan is reinstitution of the census long form; however, the costs and benefits of other options—such as implementation of a one-year ACS, operating simultaneously but not bundled with the census just as the C2SS operated in 2000—need to be developed and presented for review so that decisions on the ACS can be fully informed.12

Recommendation 4.5: The Census Bureau should identify the costs and benefits of various approaches

12  

The Office of Inspector General of the Census Bureau’s parent agency, the U.S. Department of Commerce, has expressed similar concerns. “If the Bureau does not receive sustained ACS funding throughout the decade, it may be unable to eliminate the long form for 2010”; consequently, the Census Bureau’s planning for 2010 should “include a contingency plan for use of the long form” (U.S. Department of Commerce, Office of Inspector General, 2002:iv).

 

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

to collecting characteristics information should funding for the full ACS not be forthcoming. These costs and benefits should be presented for review so that decisions on the ACS and its alternatives can be fully informed.

4–F TOPICS FOR FURTHER RESEARCH AND DESIGN CONSIDERATION

A substantial agenda of outstanding operational and methodological issues should be addressed in order to ensure a fully operational ACS. Some of these issues should be tackled in the near future in order to generate the maximum benefits from use of the ACS as part of an integrated framework of estimates.

In addition to the research and design issues we raise here, other issues are described in other sections of this report. In particular, reconciliation of the census and ACS definitions of what constitutes residence at a particular location deserves prompt consideration (Section 5-B.3). Likewise, the effects on response of the mode in which the ACS is administered (Section 5-D.2) merit further examination.

4–F.1 Group Quarters

The intent of the census long form is to provide information on characteristics of the entire population. This means not only the population residing in housing units but also those living in group quarters, such as college dormitories, military barracks, prisons, and medical and nursing facilities. Nonresponse to the census long form and the need to impute for nonresponse may detract somewhat from the overall reliability of census long-form data, but those data do at least allow users to make some inferences about the group quarters population. Accordingly, the complete elimination of the census long form—and the possible loss of data on the group quarters population—is an obvious concern of some census stakeholders.

In its draft operational plan, the Census Bureau has indicated that the ACS will be administered to a 2.5 percent sample each year from the Bureau’s group quarters roster (U.S. Census Bu-

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

reau, 2003c). It remains to be determined how adequate this may be for monitoring this important population group, especially for small geographic areas and small demographic population groups. In Section 5-B.2, we recommend a complete reexamination of the Census Bureau’s approach to enumerating the group quarters population. Continuing research and planning to ensure that this population is adequately covered in the ACS would not only contribute to a better enumeration but also bolster the case for the ACS’ unique role relative to other federal household surveys.

4–F.2 Voluntary versus Mandatory Response

The law governing conduct of the census imposes penalties on “whoever, being over eighteen years of age, refuses or willfully neglects … to answer, to the best of his knowledge, any of the questions on any schedule submitted to him in connection with any census or survey” enabled in other parts of the census code (13 USC § 241(a)).13 In addition, it is a crime to willingly give false answers to such censuses or surveys (13 USC § 241(b)). Accordingly, census mailings in 2000, as in previous years, prominently featured notices that “your response is required by law.”

The Census Bureau has argued that because the ACS is intended to replace the mandatory census long form it should be conducted on the same mandatory basis as the census. The General Accounting Office has concurred that the Bureau has statutory authority to conduct the ACS and to require responses (U.S. General Accounting Office, 2002b). The distinction between voluntary and mandatory completion is significant because it is believed that the words “required by law” on the census forms are effective in raising response rates.

However, early congressional discussion of the nature and content of the ACS led individual members of Congress to suggest that the ACS be conducted on a voluntary basis. Accordingly, the Census Bureau conducted part of the 2003 Supplementary Survey (the prototype ACS) on a voluntary basis; this test included replacing the phrase “required by law” with a more

13  

However, the census code does provide that respondents cannot be compelled to disclose their religious beliefs or affiliation (13 USC § 241(c)).

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
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generic appeal (U.S. Census Bureau, 2003c). [Rather than alter the instruments and scripts used in telephone or personal visit follow-up on a case-by-case basis, the Census Bureau conducted both types of follow-up using the voluntary participation language.] The response rates, including item nonresponse rates, on the voluntary surveys were compared with results from those obtained one year earlier in the 2002 Supplementary Survey.

Preliminary test results were publicly released by the Census Bureau in December 2003 (U.S. Census Bureau, 2003f); a fuller report and analysis is indicated as pending. The Bureau found that mail response dropped by over 20 percentage points when response was changed from mandatory to voluntary; based on the decline, the Bureau projects that a voluntary ACS would increase the annual cost of the survey by at least $59.2 million (U.S. Census Bureau, 2003f:vi). The Bureau also found evidence that participation in a voluntary-response survey was worse in areas that had low mail response to the 2000 census, leading the Bureau to conclude that voluntary methods might “compromise [its] ability to produce reliable data for these areas and for small population groups such as Blacks, Hispanics, Asians, American Indians, and Alaska Natives” (U.S. Census Bureau, 2003f:vi). If respondents decided to fill out the questionnaire, the survey results indicated that the voluntary designation did not degrade responses to individual items; voluntary and mandatory methods generally resulted in comparable levels of item nonresponse.

The mandatory versus voluntary distinction is an important one to resolve. The Census Bureau should continue work to assess the impact on nonresponse follow-up costs based on the change (likely, a decrease) in mail response if the full ACS is labeled voluntary rather than mandatory.

4–F.3 ACS as Both a Census Process and a Federal Survey

When fully implemented, the ACS will occupy a unique niche among the statistical data series collected by the federal government. Because it is intended to replace the census long form, the ACS should properly be viewed as a parallel component of the census process. It will be charged with producing the small-area and small-demographic-group data required for many legal and

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

regulatory purposes and used in many research applications. In its sweep, the ACS will require development of a technical infrastructure on par with that for the decennial census itself (see Chapter 6). Pending resolution of the debate described in the previous section, it may also bear the notice that responses to the survey are required under the law. All that said, the ACS could also be properly viewed as one of many surveys fielded by the federal government on a number of topics. This dual role of the ACS—census component and federal survey—raises concerns that will require attention in coming years.

Primary among these concerns is the substantive overlap between the ACS and other federal surveys such as the Survey of Income and Program Participation, the American Housing Survey, and—especially—the Current Population Survey (CPS). As the Census Bureau works with Congress to secure ACS funding, the panel recognizes that it is virtually inevitable that the question will be asked as to whether other surveys might be cut back or eliminated to help pay for the ACS (or vice versa). In our assessment, a fully operational ACS is not immediately exchangeable with other surveys. For instance, as the potential basis for an estimate of the poverty rate, the ACS has the advantage of larger sample size but does not cover socioeconomic and poverty-specific questions with the same depth as the CPS. The CPS has the further advantage of years of experience in soliciting detailed economic information; face-to-face interviewers acquire fuller knowledge of the survey content area and may be able to assist CPS respondents in interpreting survey questions in ways that the broader-focus ACS interviewers may not be able to match. It is decidedly premature to offer any sort of guidance on whether the ACS or another federal survey should be preferred in given situations. The panel suggests further evaluation and exploration of relative data quality in topic areas where the ACS overlaps with other federal surveys. Research should also consider ways in which the ACS could support or supplement other federal surveys, including possibilities for using recently-collected ACS characteristics data to refine the sampling frames from which other surveys are drawn (for instance, targeting surveys to low- or high-income areas).

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
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The second major concern regarding the dual role of the ACS is how the ACS will be treated within the census hierarchy. For cost savings, the ACS and short-form-only census plans should be coordinated in order to avoid redundant effort and to “piggyback” on existing structures when possible (e.g., to perform data capture using the same optical character recognition technology and equipment). Since the panel issued its second interim report, the Census Bureau transferred ACS authority and activities from its Demographic Programs directorate to the Decennial Census directorate, the same division that plans and operates the decennial census process (see Box 2.2). The full implications of this organizational move remain to be seen. The panel suggests, however, that the Census Bureau not lose sight of the inherent sample-survey nature of the ACS. While its weighting, editing, and imputation techniques may be similar to to those used in census operations (and, in particular, to past long-form implementations), they should also differ when appropriate and not be constrained to treat census and ACS returns in the exact same manner. It may also be useful, in the future, for the ACS to leave open the possibility for experimental components such as occasionally occur in federal surveys. These experimental components could include one-shot (or periodic) modules of questions on particular topics such as crime victimization or health care or on items of interest to a particular state or region. Experimental components might also include more general tests of proposed survey practices, such as was done in the test of voluntary versus mandatory response.

4–F.4 Revisiting Sampling Strategies

The basic ACS sampling strategy is simple: each month a systematic sample of approximately of the addresses on the Master Address File is taken, with one-third of mail and telephone nonrespondents randomly chosen for in-person follow-up. A number of variations on this basic strategy are either currently designed or under consideration for later implementation in the ACS by the Census Bureau. These additional possibilities are: (1) oversampling of governmental units with small populations, such as small towns, (2) oversampling of minority areas, and

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

(3) differential sampling of areas with poor initial mail and telephone response. We briefly comment on each of these possibilities and some additional methods not currently contemplated for implementation.

With respect to oversampling of small areas, the Census Bureau intends to use some version of the decennial census long-form design. In the 2000 census, sampling rates were 1 in 2 for governmental areas (counties, towns, townships, and school districts) with fewer than 800 occupied housing units (fewer than about 2,100 people); 1 in 4 for governmental areas with 800–1,200 occupied housing units (about 2,100–3,100 people); 1 in 6 for census tracts with fewer than 2,000 occupied housing units (fewer than about 5,200 people); and 1 in 8 for larger census tracts. The justification for this plan in the decennial census was originally to support reliable estimates of per capita income for small governmental units for use in fund allocation as part of general revenue sharing. However, this oversampling has been retained past the elimination of general revenue sharing because it tends to make coefficients of variation more equal across areas with different population sizes. Undoubtedly, that is the current justification for oversampling in the ACS. However, a new set of sampling rates may serve that purpose more effectively, and therefore, after the ACS has been in operation for a short while, it would be useful to compute the coefficients of variation for all responses on the ACS questionnaire for areas with different population sizes, to determine whether a different strategy might prove to be superior with respect to this objective.

For oversampling of minority areas, the Census Bureau has mentioned an interest in increasing the ACS sampling rate in areas with a high percentage of minority residents in order to provide estimates with lower coefficients of variation for important statistics historically related to racial and ethnic disparities. While the panel believes that this is justifiable, it should be understood that the historically lower mail return rates for minority populations could result in additional nonresponse follow-up costs for the ACS.

In terms of the differential sampling of areas with poor initial mail and telephone response, it is true that without it these areas will have much larger coefficients of variation than areas with

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

high mail and telephone rates. Therefore, efforts to balance these coefficients of variation are justified.

Clearly, the ACS could be modified in many ways to better satisfy various purposes. While most of the above possibilities have various disadvantages that might argue against their implementation, it would be very helpful for the Census Bureau to provide arguments to help justify the current design. These are topics that need little or no additional data collection or field work to further develop. Rather, what is needed is summary information that is already available from the ACS in the test sites. We encourage the Census Bureau to provide some analysis along these lines.

4–F.5 Interaction with Intercensal Population Estimates and Demographic Analysis Programs

One high-priority research area should be the development of models that combine information from other sources—such as household surveys, administrative records, census data, and the like—with ACS information. One prominent example of this is the interplay of ACS estimates and the Census Bureau’s population estimates program. At this point, it is planned that estimates from the ACS are to be controlled to postcensal population estimates at the county level and some degree of demographic aggregation. However, this should not be considered a one-way street. It is also possible for the ACS to be used to provide the population estimates program with improved estimates of internal and external migration, fertility, household size, and vacancy status. The resulting improved population estimates could then be used as improved marginal totals to which to control ACS estimates. Because the ACS also provides direct information on population size, a joint estimate from population estimates and from the ACS is conceivable. The Census Bureau should (1) conduct research on how the ACS can be used to improve intercensal population estimates, and (2) examine how existing household surveys could change their poststratification practices (controlling totals by age, race, and sex) given the collection of ACS data.

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

The potential for the ACS to provide improved estimates of internal and external migration also suggests the importance of exploring possible interactions between the ACS and population estimates derived by demographic analysis. Demographic analysis uses aggregate data on birth, death, immigration, and emigration to produce population estimates by age, sex, and race. It was a key benchmark used to evaluate coverage in the 2000 census, but it has significant limitations. First, estimates of immigration and emigration—particularly those of undocumented immigration—are inherently difficult to produce with precision. Second, existing administrative records used to generate demographic analysis counts facilitate only the most basic racial comparisons—white and black—but do not permit direct estimation of Hispanics and other groups. The Census Bureau should consider ways in which the ACS might inform demographic analysis estimates, including more refined estimators of the size of the foreign-born population and of internal migration. We discuss further possible improvements for demographic analysis in 2010 in Section 7-B.14

Other possibilities—for instance, using ACS and household survey information jointly in regression models to provide improved estimates of the frequency of crime or unemployment—could also be fruitfully addressed as a research topic.15 Another high-priority research area should be identification of better procedures for weighting and imputation, to address nonresponse and undercoverage in the ACS; the hope would be to develop procedures that are, in a sense, optimized for ACS survey data, and not simply borrowed from procedures used on the decennial census long form.

14  

The methods by which the ACS data could be used to improve demographic analysis could also be applicable to improvements of intercensal population estimates for the nation as a whole (National Research Council, 2000b; Citro, 2000).

15  

The use of models that combine information from other sources has implications for the sample designs of the major household surveys and is a future research topic of great potential interest. Use of these models and connections to external programs such as the ACS may permit other household surveys to reallocate sample to areas in which estimates are less reliable.

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×
4–F.6 Research on General Estimation Issues

The challenges of implementing the data collection for the ACS have understandably been given the highest priority at the Census Bureau. As a result, relatively straightforward estimation methods have been proposed for use in the short term, deferring estimation improvements for later. Unfortunately, this has meant that little research has been done on alternative approaches to estimation. We mention here some issues that should be examined by the Census Bureau once data collection is under control:

  • Alternatives to moving averages. Moving averages are easy to implement and have well-understood properties, including variance reduction. However, they will reduce large deviations that obtain for shorter periods of time than the smoothing window. There are methods for reducing this feature of moving averages that still retain much of the variance reduction benefit.16

  • Controlling versus combination. Current plans are to control ACS population estimates at the county and major demographic group level to postcensal population estimates. For initial implementation, this is a reasonable approach to take, since it will likely improve the quality of the ACS population estimates. However, the use of the ACS in combination with information from various data sources—including census data, data from household surveys, and data from administrative records—needs to be a two-way street, as the ACS will provide independent information on population size and various characteristics information formerly obtained from the long form. Specifically with respect to population size, the ACS will produce estimates at the county and major demographic group level that will have relatively large variances for most smaller counties, but because they are independent, they could still be used to improve postcensal population estimates. This will be more certain the further one moves away from a census year, as postcensal population estimates are increasingly

16  

Two possibilities that could be examined are state-space time-series models and spline smoothers.

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

variable as one moves further into each decade. In addition, the ACS data on population would not need to be used directly. Instead, data from the ACS could be applied to components of the postcensal estimates program, in particular estimates of interstate mobility, fertility, and household occupancy. Finally, there is the much more demanding vision of the ACS underlying a small-area estimates program, whereby information from the above sources is used in conjunction with the ACS to produce a wide variety of small-area information of higher quality than could be provided by any individual data source. Given the varying quality of data from ACS and other sources, ACS data should not simply be controlled to data from these other sources; instead, hierarchical models should be used that will let the data from the various sources determine the degree to which estimates are combined. This latter vision in totality is certainly beyond the current research literature in terms of complexity of application, especially since many of the proposed data sources might be inconsistent. However, initial efforts should be undertaken since the methods to carry out simple versions of this possibility currently exist and are regularly used in other applications.

  • Weighting and imputation methods. The Census Bureau currently intends to use ten or so different weighting methods to accommodate: (1) the sample design of the ACS, (2) the use of data from different months (and modes) of response to compute the estimates for a given month and area, (3) whole household nonresponse, (4) individual unit nonresponse, (5) individual item nonresponse, and (6) undercoverage. These methods were adopted because of their current use (when relevant) in processing the decennial census short and long forms, and because of their resulting recognized benefits and ease of implementation in that very similar setting. Some of these weighting approaches are entirely appropriate for the ACS, and some are unique to the ACS as they are meant to address differential mode effects and the more complex sample design of the ACS relative to the long form. However, the current

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
×

use of sequential hot-deck imputation for the treatment of individual item nonresponse, and the use of variance estimates that ignore the contribution of item nonresponse, are methods that are no longer representative of the current state of the art. Furthermore, it is not clear that nonresponse and undercoverage for the ACS will be sufficiently similar to these problems for the long form that these various long-form weighting methods should be utilized in the ACS without additional supporting research. The particular problem of the treatment of item nonresponse is becoming increasingly important given the degree of nonresponse experienced in the 2000 census.

Suggested Citation:"4 American Community Survey." National Research Council. 2004. Reengineering the 2010 Census: Risks and Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10959.
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At the request of the U.S. Census Bureau, the National Research Council’s Committee on National Statistics established the Panel on Research on Future Census Methods to review the early planning process for the 2010 census. This new report documents the panel’s strong support for the major aims of the Census Bureau’s emerging plan for 2010. At the same time, it notes the considerable challenges that must be overcome if the bureau’s innovations are to be successful. The panel agrees with the Census Bureau that implementation of the American Community Survey and, with it, the separation of the long form from the census process are excellent concepts. Moreover, it concurs that the critically important Master Address File and TIGER geographic systems are in dire need of comprehensive updating and that new technologies have the potential to improve the accuracy of the count. The report identifies the risks and rewards of these and other components of the Census Bureau’s plan. The report emphasizes the need for the bureau to link its research and evaluation efforts much more closely to operational planning and the importance of funding for a comprehensive and rigorous testing program before 2010.

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