[Federal Register Volume 65, Number 119 (Tuesday, June 20, 2000)]
[Notices]
[Pages 38374-38398]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 00-15348]



[[Page 38373]]

-----------------------------------------------------------------------

Part V





Department of Commerce





-----------------------------------------------------------------------



Bureau of the Census



-----------------------------------------------------------------------



Accuracy and Coverage Evaluation; Statement of the Feasibility of Using 
Statistical Methods To Improve the Accuracy of the Census 2000; Notice

Federal Register / Vol. 65, No. 119 / Tuesday, June 20, 2000 / 
Notices

[[Page 38374]]


-----------------------------------------------------------------------

DEPARTMENT OF COMMERCE

Bureau of the Census


Accuracy and Coverage Evaluation; Statement on the Feasibility of 
Using Statistical Methods To Improve the Accuracy of Census 2000

AGENCY: Bureau of the Census, Department of Commerce.

ACTION: Notice.

-----------------------------------------------------------------------

SUMMARY: The Director of the Census has issued Accuracy and Coverage 
Evaluation; Statement on the Feasibility of Using Statistical Methods 
to Improve the Accuracy of Census 2000, his statement on the 
feasibility of using modern statistical methods to correct Census 2000 
counts. The document sets forth the rationale for the Census Bureau's 
preliminary determination that (1) statistically corrected census data 
can be produced within the time frame required by law and (2) that 
statistically corrected data will be more accurate. The Secretary has 
adopted the Director's analysis and conclusions in a written decision 
forwarded to the Director. For public information, set forth below is 
Accuracy and Coverage Evaluation; Statement on the Feasibility of Using 
Statistical Methods to Improve the Accuracy of Census 2000, as well as 
three related memoranda (the Director's memorandum transmitting the 
document to the Secretary, the Secretary's memorandum to the Director, 
and a supporting legal opinion of the Commerce Department's General 
Counsel).

    Authority: 13 U.S.C. 141, 13 U.S.C. 195.

William G. Barron,
Deputy Director.
June 12, 2000.
MEMORANDUM FOR The Honorable William Daley, Secretary of Commerce
Through: Robert Shapiro, Under Secretary for Economic Affairs
From: Kenneth Prewitt, Director
Subject: Accuracy and Coverage Evaluation: Statement on the Feasibility 
of Using Statistical Methods to Improve the Accuracy of Census 2000

    Attached is my statement on the feasibility of using modern 
statistical methods to correct Census 2000 counts as stipulated by the 
U.S. Supreme Court's decision in Department of Commerce v. United 
States House of Representatives (January 1999). This statement was 
prepared after extensive discussions with the U.S. Census Bureau's 
senior staff and review of all relevant documents.
    The Census Bureau is committed to making its data as accurate as 
possible for all uses. This document sets forth the rationale for the 
Census Bureau's preliminary determination that (1) statistically 
corrected census data can be produced within the time frame required by 
law and (2) that statistically corrected data will be more accurate.

ACCURACY AND COVERAGE EVALUATION

STATEMENT ON THE FEASIBILITY OF USING STATISTICAL METHODS TO IMPROVE 
THE ACCURACY OF CENSUS 2000

Table of Contents

Executive Summary
Background and Overview
    Uses of Decennial Census Data
    The Differential Undercount
    Summary of Census 2000 Operations
    The Accuracy and Coverage Evaluation Methodology
    The A.C.E. in Brief
    The Sample Design
    Conducting the Survey
    Dual System Estimation
Assessment of Feasibility
    The Definition of Feasibility
    Operational Feasibility
    Release of Data Products for Use in Redistricting
    Operational Considerations
    Resource Considerations
    The Census 2000 Dress Rehearsal
    Technical Feasibility
    Defining Numeric and Distributive Accuracy
    Importance of and Relationship Between the Two Types of Accuracy
    Impact of the A.C.E. on Accuracy
    Historical Experience with Coverage Measurement Surveys
    Demonstrates Feasibility
    The 1980 Census Experience
    Early Research and Development for the 1990 Census
    Litigation Challenging Decision to Halt 1990 Adjustment-Related 
Planning Activities
    Conducting the 1990 Census and Deciding Against Adjustment
    Postcensal Estimates and Survey Controls Decision
    Early Census 2000 Planning
    The Census 2000 Dress Rehearsal
    External Review
A.C.E. Implementation Issues
    Measuring Accuracy
    Assessment of Issues Emerging from 1990
    The Proper Standard to Use in Deciding Whether to Statistically 
Correct the Counts for Non-Apportionment Purposes
    Numeric v. Distributive Accuracy
    Correlation Bias
    Accuracy at Different Geographic Levels
    Consistency with Demographic Analysis
    Timing
    Level of Sampling Variance/Smoothing
    Level of Nonsampling Error/Bias
    Enhancements to the Matching Process
    Enhancements to Computer Processing
    Enhancements to Minimize Missing Data
    Homogeneity and the Synthetic Assumption
    Additional Design Changes from 1990
    Use of the Telephone in A.C.E. Interviewing
    New Treatment to Account for Movers
    Search Area for Matching
    Reporting More Than One Race
Making the Final Decision
Conclusions
Bibliography

Executive Summary

    This document sets forth the rationale for the Census Bureau's 
preliminary determination that (1) it is feasible to produce 
statistically corrected census data within the time frame required by 
law and (2) the statistically corrected data will be more accurate.
    Data from the decennial census are used to produce the state 
population totals for congressional apportionment. Additionally, 
detailed state data are used for redistricting, federal funds 
distribution, and other public and private sector purposes. Section 
141(b) of Title 13 requires the Secretary of Commerce to report state 
population totals from Census 2000 to the President by January 1, 2001. 
Section 141(c) requires the Census Bureau to report redistricting data 
directly to the states by April 1, 2001.
    The Census Bureau is committed to making its data as accurate as 
possible for all uses. In accordance with a 1999 Supreme Court ruling, 
the Census Bureau will not use statistical sampling to produce the 
state population totals used for congressional apportionment. Because 
the Census Bureau expects it can produce more accurate data by 
supplementing traditional enumeration procedures with statistical 
sampling, it plans to use these statistical methods to produce the more 
detailed data required for redistricting and federal program purposes.
    Prior to April 1, 2001, the Census Bureau will have completed an 
enumeration of the American population, including a coverage 
measurement survey, that is designed to improve the accuracy of the 
initial counts. The coverage measurement survey, called the Accuracy 
and Coverage Evaluation (A.C.E.), is based on the established 
statistical method known as Dual System Estimation (DSE) and is 
designed to correct for missed individuals or erroneous enumerations in 
the traditional enumeration. The method of Demographic Analysis will 
also be used to evaluate the completeness of population coverage in 
Census 2000 at the national level, and to assess changes from previous 
censuses.

[[Page 38375]]

    The operations used to produce the apportionment counts are 
designed with the goal of counting and correctly locating every 
individual residing in the United States on April 1, 2000, and also to 
count federal employees and their dependents living overseas as of that 
date. This goal cannot be completely and accurately realized. Every 
decennial census, from 1790 to 1990, has included in the census counts 
some who should have been excluded, and has missed some who should have 
been included. The first source of error leads to an overcount; the 
second source to an undercount. Every census for which the effect of 
these errors has been systematically measured has shown a net 
undercount--that is, the number of residents who were missed was 
greater than the number of erroneous enumerations.
    Furthermore, in studies going back to 1940, the Census Bureau has 
documented and measured not only an overall net undercount, but also a 
higher net differential undercount for the Black population than for 
the non-Black population. Studies from the 1990 census also indicate 
differentially higher net undercounts for the Hispanic population and 
American Indians on reservations, compared to the White population. 
This persistent problem of differential undercounts is the most 
significant error for the population totals obtained through the 
traditional enumeration. As part of the operations for Census 2000, the 
Census Bureau will conduct the A.C.E., which is designed to improve 
census accuracy by increasing overall coverage and reducing the 
differential undercount. The A.C.E. also corrects for the smaller, 
though not insignificant, overcount that occurs when erroneous 
enumerations are included in the census.
    The Census Bureau has determined that the A.C.E. is operationally 
and technically feasible and expects, barring unforeseen operational 
difficulties that would have a significant effect on the quality of the 
data, that these corrected data will be more accurate than the 
uncorrected data for their intended purposes. This determination is 
based on more than 20 years of Census Bureau research and experience 
with coverage measurement surveys using DSE and is supported by 
external experts in statistical methodology. From these years of 
experience, Census Bureau statisticians have a comprehensive 
understanding of the technical underpinnings of DSE. This understanding 
has guided the design of the A.C.E., allowing the Census Bureau to 
focus on the completeness and quality of the estimates of the 
population corrected for estimated net census error.
    It is possible, though very unlikely, that problems with census 
operations could lead the Census Bureau to conclude that the data are 
not of sufficient quality for their intended purposes. These problems 
could occur in the operations leading to production of the 
apportionment counts and/or in the operations leading to the production 
of the corrected counts. This document does not address factors that 
the Census Bureau will consider in its determination that the 
apportionment counts are of sufficient quality to be used for their 
intended purposes. Because this document does focus on the feasibility 
of using statistical methods to improve the accuracy of Census 2000 for 
purposes subsequent to the production of apportionment counts, it 
discusses the review process for the final decision on whether to 
release statistically corrected data. This review process will be based 
on a determination of whether the A.C.E. operations were conducted in a 
way that met expectations. In the fall of 2000, the Census Bureau will 
present this review process to the statistical community and other 
interested parties.

Background and Overview

    Census data are critically important in achieving equitable 
political representation and fair allocation of resources. Finding and 
enumerating approximately 275 million individuals in the correct 
location is, of course, an extremely challenging task. The traditional 
decennial census misses certain identifiable population groups at 
greater rates than others and therefore contains inherent inaccuracies. 
The Census Bureau designed the Accuracy and Coverage Evaluation 
(A.C.E.) using proven statistical methodologies to correct for this 
differential undercount and thereby make the census more accurate.

Uses of Decennial Census Data

    The Constitution requires that a census of the nation's population 
be taken every 10 years to reapportion seats in the House of 
Representatives,\1\ but the information provides more than just state-
by-state population totals. State and local governments use census data 
to draw legislative districts of equal population to comply with the 
constitutional ``one-person-one-vote'' mandate and the statutory 
requirements of the Voting Rights Act. The federal government 
distributes billions of dollars in grants according to population-based 
formulae that rely on census data. Federal, state, local and tribal 
officials study the patterns of detailed census data before 
constructing hospitals, highways, bridges, and schools. Businesses, 
large and small, have come to depend on the Census Bureau's population, 
income, education, and housing data to make informed decisions about 
locating new offices, shops, and factories, and finding markets for new 
products and services. Census data also serve as definitive benchmarks 
for many of the household surveys conducted by federal agencies.
---------------------------------------------------------------------------

    \1\ Constitution, Art. I, Sec. 2, cl. 3.
---------------------------------------------------------------------------

    As will be explained in more detail below, the Census Bureau has 
designed the A.C.E. so that it will produce statistically corrected 
census data down to the block level. Census blocks are the ``building 
blocks'' employed by users of census data. The Census Bureau does not 
define the aggregations employed by data users; it provides the data 
that users can tabulate as needed for their programmatic purposes. For 
example, an administrator distributing funds under the Elementary and 
Secondary Education Act might need to distribute funds tabulated to 
school districts, which can range in size from large counties and 
cities to small towns and districts, while a state official responsible 
for redistricting might need to aggregate and re-aggregate census 
blocks into many different configurations to satisfy the requirements 
of the Voting Rights Act, 42 U.S.C. Sec. 1971 et seq.

[[Page 38376]]

    The A.C.E. was designed to accommodate the needs of data users by 
allowing them to aggregate census blocks as appropriate for their 
particular program purposes. The accuracy of aggregated census data is 
more important than the accuracy of any particular block because data 
users rely on aggregated data, not block-level data.\2\ Different types 
of accuracy and how they can be assessed at various levels of 
aggregation are reviewed below.
---------------------------------------------------------------------------

    \2\ The National Academy of Sciences agrees that accuracy at the 
block level is not an appropriate criterion of accuracy, that 
accuracy should be evaluated at aggregated levels. See Andrew A. 
White and Keith F. Rust, eds., Preparing for the 2000 Census: 
Interim Report II (Washington, D.C.: National Academy Press, 1997), 
11-12.
---------------------------------------------------------------------------

    This recitation of the uses of census data illustrates the 
importance of taking as accurate a census as possible by reducing the 
differential undercounts of geographic areas and demographic groups. 
The belief that the census should be as accurate as possible has 
motivated the Census Bureau for more than 20 years to develop 
techniques to reduce the differential undercount.

The Differential Undercount

    The Census Bureau has documented and measured a substantial 
differential undercount since the 1940 census.\3\ After the 1940 
census, Census Bureau statisticians and academic researchers refined a 
statistical technique known as Demographic Analysis, a technique that 
measures coverage trends as well as differences in coverage by age, 
sex, and race. Demographic Analysis uses records and estimates of 
births, deaths, immigration, emigration, and Medicare enrollments to 
develop estimates of the population at the national level, 
independently from the census. Demographic Analysis, though not without 
its errors, reveals the persistence of the differential undercount that 
exists between the Black and the non-Black populations. The following 
table illustrates this differential:
---------------------------------------------------------------------------

    \3\ Bureau of the Census, ``Report to Congress--The Plan for 
Census 2000,'' originally issued July 1997, revised and reissued 
August 1997, 2-6.

                 Demographic Analysis Estimates of Percentage Net Undercount, by Race: 1940-1990
----------------------------------------------------------------------------------------------------------------
                                                   1940       1950       1960       1970       1980       1990
----------------------------------------------------------------------------------------------------------------
Percent:
    Total.....................................        5.4        4.1        3.1        2.7        1.2        1.8
    Black.....................................        8.4        7.5        6.6        6.5        4.5        5.7
    Non-Black.................................          5        3.8        2.7        2.2        0.8        1.3
    Percentage Point Difference:
    Black/Non-Black...........................        3.4        3.6        3.9        4.3        3.7        4.4
----------------------------------------------------------------------------------------------------------------

    Source: J.G. Robinson and others, ``Estimates of Population 
Coverage in the 1990 United States Census Based on Demographic 
Analysis,'' Journal of the American Statistical Association 88, 
(September 1993): 1065.
    The 1990 census revealed that the Black population was not the only 
group undercounted differentially. Children were much more likely than 
adults to have been undercounted in the 1990 census. While children 
under the age of 18 represented 26 percent of the total national 
population that year, they accounted for 52 percent of the net 
estimated undercount as estimated by the 1990 Post-Enumeration Survey 
(PES).\4\ Another characteristic that affected the likelihood of being 
missed in the census was tenure, whether one rents or owns. Renters 
were more likely to have been left out of the 1990 count. The 1990 PES 
found higher undercounts among renters than for owners.\5\ As the chart 
below demonstrates, a substantial differential undercount also was 
estimated in 1990 for Hispanics and American Indians on reservations:
---------------------------------------------------------------------------

    \4\ Ibid., 3.
    \5\ Howard Hogan, ``The 1990 Post-Enumeration Survey: Operations 
and Results,'' Journal of the American Statistical Association 88 
(September 1993): 1054, Table 3.

---------------------------------------------------------------------------

[[Page 38377]]

[GRAPHIC] [TIFF OMITTED] TN20JN00.006

    Within each demographic group, the undercount for renters was 
considerably higher than for owners. For example, the estimated 
undercount was 6.5 percent for Black renters versus only 2.3 percent 
for Black owners.\7\
---------------------------------------------------------------------------

    \6\ Bureau of the Census, ``Assessment of Accuracy of Adjusted 
Versus Unadjusted 1990 Census Base for Use in Intercensal 
Estimates,'' Report of the Committee on Adjustment of Postcensal 
Estimates,'' 7 August 1992, Attachment 3A, Table 2, later referred 
to as CAPE; and Bureau of the Census, ``Report to Congress--the Plan 
for Census 2000,'' 4.
    \7\ Hogan, ``The 1990 Post-Enumeration Survey: Operations and 
Results,'' 1054, Table 3.
---------------------------------------------------------------------------

    The differential undercount is a longstanding problem and one that 
the Census Bureau has not been able to solve despite increased efforts 
and resources. The National Academy of Sciences has calculated that the 
per housing unit cost of the census, in 1990 constant dollars, 
increased from less than $10 per housing unit in 1960, to $11 per 
housing unit in 1970, to $20 per housing unit in 1980, and to $25 per 
housing unit in 1990.\8\ This steady increase in unit cost from 1960 to 
1990, in large part due to increased efforts to reduce coverage errors, 
did not result in any appreciable reduction in the differential 
undercount.
---------------------------------------------------------------------------

    \8\ Barry Edmonston and Charles Schultze, eds., Modernizing the 
U.S. Census (Washington, D.C.: National Academy Press, 1995), 44. 
The cost for Census 2000 is currently estimated to be over $50 per 
housing unit in current dollars, indicating the increasingly greater 
cost of taking a census using traditional methods.
---------------------------------------------------------------------------

    The differential undercount clearly affects census accuracy. When 
identified areas and demographic groups are differentially 
undercounted, the relative population shares across states and sub-
state areas are incorrect. Census data also provide the foundation for 
a large number of federal demographic statistics and household 
statistical surveys. These data are also extensively used by the 
private sector. Inaccuracies in the decennial census are carried over 
into these many other statistical series, and therefore, the persistent 
differential undercount has far-reaching consequences across public and 
private sector programs based on census data.

Summary of Census 2000 Operations

    The Supreme Court determined in 1999 that Title 13 statutorily 
precludes the use of sampling to produce congressional apportionment 
counts.\9\ Accordingly, the plan for Census 2000, as outlined in the 
Updated Summary: Census 2000 Operational Plan (February 1999), is to 
produce apportionment numbers without the use of statistical sampling 
by January 1, 2001. Rather than conducting the Integrated Coverage 
Measurement (ICM) survey \10\ to produce statistically corrected 
numbers as part of the original Census 2000 plan, the plan now includes 
the A.C.E., which will produce statistically corrected numbers for non-
apportionment uses of the data.
---------------------------------------------------------------------------

    \9\ Department of Commerce v. House of Representatives, 119 
S.Ct. 765 (1999).
    \10\ The Census Bureau's original plan to use sampling was to 
conduct an Integrated Coverage Measurement (ICM) survey to produce a 
one-number census through the use of statistical sampling (``Report 
to Congress--The Plan for Census 2000,'' 29-32). The Census Bureau 
dropped its plans to conduct an ICM after the Supreme Court ruled 
that sampling could not be used to produce the apportionment counts.
---------------------------------------------------------------------------

    Within the constraint of the 1999 Supreme Court decision, the 
Census Bureau is committed to producing the most accurate data possible 
without the use of sampling for purposes of apportionment. The 
constraint does not apply to non-apportionment uses, and the Census 
Bureau also remains committed to producing the most accurate data 
possible for these other uses by implementing the A.C.E. As a prelude 
to the discussion of the A.C.E., this paper will briefly review basic 
census operations to be conducted prior to the A.C.E. A more extensive 
explanation of the operations for Census 2000 can be found in the 
Census 2000 Operational Plan.
    The Census Bureau uses three basic data collection methods: 
mailout/mailback (where the Census Bureau mails questionnaires to 
housing units on the address list and the residents mail them back), 
update/leave (where Census Bureau workers deliver questionnaires at the 
same time they update the address list, and the residents mail them

[[Page 38378]]

back), and list/enumerate (where Census Bureau enumerators create the 
address list while canvassing their assignment areas and conducting 
interviews with respondents). Individuals can also respond to the 
census through the Internet or by telephone. The Be Counted program 
provides an additional means for people to be included in the census by 
allowing them to fill out a blank form made available in various public 
locations. Special enumeration procedures are followed for remote parts 
of Alaska, for locations containing a concentration of persons with a 
transient lifestyle (e.g., trailer parks, marinas, and campgrounds), 
for group quarters (e.g., prisons and long-term care facilities), and 
for people with no usual residence.
    After allowing a reasonable amount of time for respondents to mail 
back their questionnaires, the Census Bureau conducts an operation 
called nonresponse followup (NRFU), which involves conducting a field 
followup of housing units that do not return their questionnaires by 
mail. A census enumerator will make up to six attempts to contact 
housing units that appear occupied to secure an interview. If an 
interview cannot be obtained, the enumerator attempts to interview a 
proxy respondent, that is, a neighbor, rental agent, building manager, 
or other knowledgeable individual.
    A number of other operations are being implemented to ensure as 
complete coverage as possible in the initial enumeration. Computer 
edits are performed on mail-return questionnaires to identify those 
that may contain missing persons and those that contain large 
households (more than six persons). Interviewers conduct telephone 
interviews with these households during the coverage edit followup 
operation in order to obtain accurate data about the persons residing 
there. Another operation, coverage improvement followup, is conducted 
after NRFU. This operation includes an interviewer recheck of housing 
units classified as vacant or nonexistent during NRFU to ensure that no 
units have been misclassified. Finally, all major operations of the 
Census 2000 plan are subjected to enhanced quality assurance (QA) 
activities designed to detect and correct errors before they affect 
accuracy or data quality.
    The Census Bureau also designed and implemented an enhanced 
marketing and partnership program that provides an integrated 
communications effort to increase both awareness of the decennial 
census and public cooperation. The marketing program is designed around 
the first-ever paid advertising campaign, including a national media 
campaign aimed at increasing mail response, targeted advertising 
directed at raising mail response among historically undercounted 
populations, and special advertising messages and campaigns targeted to 
hard-to-enumerate populations. In the partnership program, the Census 
Bureau is working nationwide with state and local partners to encourage 
all individuals to respond to the census.
    After the data collection efforts have been completed, the data are 
processed through a number of computer operations for unduplication of 
multiple responses for the same housing unit and for editing of 
inconsistent or missing responses. For items that are not reported by 
respondents, the Census Bureau uses the statistical process of 
imputation to determine a response. The data are then tabulated, and 
the tabulations and other statistical aggregations are released.

The Accuracy and Coverage Evaluation Methodology

    Following the initial census, the Census Bureau will conduct the 
A.C.E. Key components of the A.C.E. include the sample design, the 
survey itself, and the Dual System Estimation (DSE) used to compute the 
estimates of the true population.\11\
---------------------------------------------------------------------------

    \11\ A more extensive description of the A.C.E. can be found in 
Howard Hogan's paper, ``Accuracy and Coverage Evaluation: Theory and 
Application'', prepared for the February 2-3, 2000, DSE Workshop of 
the National Academy of Sciences Panel to Review the 2000 Census; 
and Bureau of the Census, ``Accuracy and Coverage Evaluation: 
Overview of Design'', by Danny R. Childers and Deborah A. 
Fenstermaker, DSSD Census Procedures and Operations Memorandum 
Series S-DT-02, 11 January 2000.
---------------------------------------------------------------------------

The A.C.E. in Brief
    The A.C.E. methodology planned for Census 2000 involves comparing 
(matching) the information from an independent sample survey to initial 
census records. In this process, the Census Bureau conducts field 
interviewing and computerized and clerical matching of the records. 
Using the results of this matching, the Census Bureau will apply the 
statistical methodology of DSE (described below) to develop coverage 
correction factors for various population groups. The results will then 
be applied to the census files to produce all required Census 2000 
tabulations, other than apportionment. The A.C.E. can be summarized as 
follows:
    <bullet> Select a stratified random sample of blocks for the A.C.E.
    <bullet> Create an independent list of housing units in the sample 
of A.C.E. blocks.
    <bullet> Begin conducting telephone interviews of mail return 
housing units on a subset of the independent list.
    <bullet> After the initial census nonresponse followup, conduct a 
personal visit interview at every housing unit on the independent list 
not already interviewed by telephone.
    <bullet> Match the results of the A.C.E. interview to the initial 
census.
    <bullet> Resolve cases that may not match but that require 
additional information by conducting a personal visit followup 
interview.
    <bullet> Use information from other similar people to impute 
missing information.
    <bullet> Categorize the A.C.E. data by age, sex, tenure, and other 
appropriate predefined variables into groupings called post-strata.
    <bullet> Calculate the coverage correction factors using DSE, that 
is, determine the extent to which people in each post-stratum have been 
over- or undercounted by the initial census.
    <bullet> Apply the coverage correction factors to correct the 
initial census data.
    <bullet> Tabulate the statistically corrected census results.
The Sample Design
    For the 2000 A.C.E., the Census Bureau selected a stratified random 
sample of blocks designed to be representative of racial and ethnic 
composition; tenure (owner or renter); and other variables. The sample 
consists of approximately 11,800 block clusters with approximately 
314,000 housing units. The sample is designed to provide sufficient 
precision to estimate the true population for groupings of the 
population known as post-strata. Each person belongs to one and only 
one post-stratum. Post-strata are constructed with the goal of grouping 
individuals who have a similar probability of having been included in 
the initial census. Census 2000 post-stratification variables include 
race, ethnicity, age, sex, tenure, mail return rate, and metropolitan 
status/census enumeration method. For example, one post-stratum would 
include non-Hispanic Black males, aged 18-29, in non-owner units, in 
mailout/mailback areas of metropolitan statistical areas with 500,000 
or more population, in tracts with a low mail return rate in the 
census. By comparing the estimated true population based on the dual 
system estimate for each post-stratum to the number of individuals 
counted in the initial census enumeration for each post-stratum, the 
Census Bureau estimates over- and undercounts for each post-stratum.

[[Page 38379]]

Conducting the Survey
    Essential to the proper conduct of the A.C.E. is the need to ensure 
that the A.C.E. and the initial census are operationally independent. 
Independence requires that the probability of a particular household or 
person being included in the A.C.E. is not affected by the initial 
census operations and that the probability of people being included in 
the initial census is not affected by A.C.E. operations. Such 
independence is a critical criterion for DSE.
    The A.C.E. independent interview is conducted by separately hired 
and trained staff through the use of Computer Assisted Personal 
Interviewing (CAPI) either by telephone or in person. CAPI is a method 
of data collection using a laptop computer in which the questions to be 
asked are displayed on the screen and responses are entered directly 
into the computer. The Census Bureau expects that the use of CAPI will 
improve the accuracy of the A.C.E. interview. To get an early start for 
the A.C.E. interviewing, where possible, a telephone interview using 
CAPI may be conducted for households where the census questionnaire has 
been completed and for which a telephone number was obtained. This 
activity is carried out concurrently with the initial census followup 
of nonresponse households. The door-to-door interviewing with CAPI does 
not begin until the initial census nonresponse followup is nearly 
completed in a given block cluster. The A.C.E. enumerators will attempt 
to secure an in-person interview with a household member. If the 
interview cannot be obtained, the enumerator will interview a proxy 
respondent.
    After the A.C.E. independent interviews have been completed, 
computer matching between the initial census and the A.C.E. person 
records is carried out, followed by a clerical matching operation using 
an automated review system. The matching process allows the Census 
Bureau to determine who may have been missed by the initial census or 
to determine erroneous enumerations. It should be noted that the census 
can miss either entire households or individuals within households. 
This is also the case for erroneous enumerations.
    The Census Bureau has carefully designed the A.C.E. to minimize 
matching errors. Incorrect matching generally results either from 
errors caused by incomplete, inaccurate, or conflicting data, or from 
errors where a poor match decision was made even though the data were 
sufficient. It is critical that the matching be as accurate as 
possible. Accordingly, as necessary, the Census Bureau conducts a 
personal visit follow-up operation to obtain the additional information 
needed to accurately code A.C.E. and census nonmatches. After this 
followup, the Census Bureau conducts a final clerical matching 
operation.
    Even after this intense effort, occasionally some information will 
still be missing, either person characteristics, status of enumeration 
in the initial census, or match status for A.C.E. cases that could not 
be resolved. Before any calculations can be made to determine the 
estimated true population, missing person characteristics, initial 
census enumeration status, and A.C.E. match status must be resolved. 
Missing person characteristics such as age, race, sex, and tenure are 
statistically imputed from data reported for other household members or 
from similar households in the geographic area. For unresolved cases, 
the Census Bureau uses statistical imputation methodology to impute 
probabilities of being correctly enumerated or matched. The Census 
Bureau then estimates the true population by using these results in 
Dual System Estimation.
Dual System Estimation
    DSE is an established and accepted statistical technique that is 
also referred to as ``capture/recapture.'' \12\ Because the Census 
Bureau has conducted years of research into the likelihood that people 
of varying characteristics will be included in the census enumeration 
(this likelihood is known as inclusion probability), it is able to 
divide the nation's population into post-strata. Each post-stratum is 
defined so as to contain people with a similar probability of being 
included in the initial census. At the conclusion of the A.C.E. 
processes described previously, data are available for each post-
stratum to calculate a dual system estimate.\13\
---------------------------------------------------------------------------

    \12\ Michael L. Cohen, Andrew A. White, and Keith F. Rust, 
Measuring a Changing Nation--Modern Methods for the 2000 Census 
(Washington, D.C.: National Academy Press, 1999), 31; and Kirk M. 
Wolter, ``Some Coverage Error Models for Census Data,'' Journal of 
the American Statistical Association 81 (June 1986): 338.
    \13\ Production of these estimates is discussed in more detail 
in Bureau of the Census, ``Accuracy and Coverage Evaluation Survey: 
Dual System Estimation,'' by Donna Kostanich and Richard Griffin, 
DSSD Census 2000 Procedures and Operations Memorandum Series #Q-20, 
12 January 2000.
---------------------------------------------------------------------------

    The dual system estimate is an estimate of the true population 
total for each post-stratum. The dual system estimates are then used to 
calculate a coverage correction factor for each post-stratum. The 
coverage correction factor is a ratio of the dual system estimate (the 
estimate of the true population) to the initial census count. These 
factors are then applied to correct the initial census data files. For 
example, if the coverage correction factor for non-Hispanic Black 
males, aged 18-29, in non-owner units, in mailout/mailback areas of 
metropolitan statistical areas with 500,000 or more population, in a 
tract with a low mail return rate in the census, is 1.02, then for 
every 100 such person records counted in the census in those areas, two 
numerical records will be added. Once these factors are applied, the 
corrected population estimates are created and tabulated.

Assessment of Feasibility

    Section 195 of the Census Act states that ``the Secretary shall, if 
he considers it feasible, authorize the use of sampling,'' but the term 
``feasible'' is not defined. As discussed in a legal opinion from the 
Department of Commerce's General Counsel, the Census Bureau understands 
this term in accordance with its ordinary meaning and the overall 
purposes of Title 13. It is important to note that even if Title 13 
were silent as to the obligation to use sampling if feasible, the 
Census Bureau would apply criteria similar to those described below to 
determine whether to correct the census through the use of statistical 
sampling. The Census Bureau is committed to using reliable statistical 
methods if those methods can be expected to improve the overall 
accuracy of the census.

The Definition of Feasibility

    The Census Bureau's determination that sampling is ``feasible'' is 
based on whether its use is possible, that is, compatible with other 
aspects of the census plan and with any statutory, timing, and funding 
constraints. Equally important, this determination is based on whether 
the use of sampling is expected to improve the overall accuracy of 
census data by improving overall coverage and reducing the differential 
undercount. These two components of the feasibility determination 
represent operational feasibility and technical feasibility. Can the 
Census Bureau produce the statistically corrected block-level numbers 
by the April 1, 2001, statutory deadline? Can the statistically 
corrected counts be expected to improve the overall accuracy of census 
data?
    More specifically, in the context of Census 2000, the use of 
statistical sampling is feasible to correct the census if the two 
components of feasibility, operational and technical,

[[Page 38380]]

are satisfied. Operational feasibility refers to the Census Bureau's 
ability to conduct the A.C.E. with available resources and within 
required deadlines or time frames. Technical feasibility refers to the 
Census Bureau's expectation that the A.C.E. statistical methodology, if 
carried out as planned, will improve the accuracy of the census for 
non-apportionment uses of the data. As discussed below, the Census 
Bureau's extensive experience with coverage measurement surveys, 
including its incorporation of improvements since 1990, confirms the 
conclusion that the A.C.E. is both operationally and technically 
feasible.

Operational Feasibility

    Operational feasibility refers to the Census Bureau's ability to 
conduct each major component of the census within applicable deadlines 
and with available resources. The Census Bureau expects to conduct each 
major component of the census, including the A.C.E., in time to meet 
the April 1, 2001, deadline for producing the redistricting data.
Release of Data Products for Use in Redistricting
    The Census Bureau's goal is to produce the most accurate numbers 
possible within the constraints imposed by the federal statute and 
available resources. Section 141(c) of Title 13 requires the Census 
Bureau to deliver redistricting numbers to the states by April 1, 
2001.\14\ In past decennial censuses, the Census Bureau has been able 
to release redistricting numbers to certain states prior to the federal 
deadline, enabling redistricting officials in those states to meet 
deadlines set by state statutes and constitutions. The Census Bureau 
will, as in the past, release the numbers from Census 2000 to the 
states as they are ready, giving priority to states that need to meet 
early deadlines.
---------------------------------------------------------------------------

    \14\ The Census Bureau's FY 1998 Appropriations Bill (P.L. 105-
119) requires the Census Bureau, when it releases redistricting 
numbers based on statistical methods, to also release data produced 
without the use of statistical methods at all levels of geography.
---------------------------------------------------------------------------

Operational Considerations
    The Census Bureau's detailed plan for carrying out the entirety of 
the census operation, including the A.C.E., is set forth in the 
``Master Activity Schedule'' (MAS).\15\ This plan has undergone 
thorough reviews and analyses and supports the Census Bureau's 
confidence that it can implement the A.C.E. methodology correctly and 
successfully. The Census Bureau introduced its original Census 2000 
plan in 1995. Since that time, the plan has been refined to incorporate 
testing, analysis, expert and other public input, and policy and 
programmatic changes, including the Supreme Court's January 25, 1999, 
ruling. During the last five years, the Census Bureau has put into 
place a comprehensive project management framework based on a powerful 
project management tool used by some of the world's largest private 
organizations. The use of this and other project tools, such as an 
integrated cost model and function and process modeling software, led 
to the Census Bureau's determination that it could produce the 
statistically corrected numbers by April 1, 2001. A revised Census 2000 
MAS, reflecting this determination, along with the Census 2000 
Operational Plan, were presented to the U.S. House of Representatives 
Subcommittee on the Census, as well as the Census Bureau's other 
oversight and appropriations committees and subcommittees, in March 
1999.
---------------------------------------------------------------------------

    \15\ Bureau of the Census, ``Master Activity Schedule for Census 
2000.''
---------------------------------------------------------------------------

Resource Considerations
    Resources are also relevant to a feasibility determination. Based 
on current FY 2000 appropriations and the anticipation that the 
Administration's FY 2001 budget request for Census 2000 will be 
appropriated, the Census Bureau should be able to hire sufficient staff 
and acquire the necessary equipment to complete Census 2000 and produce 
statistically corrected redistricting numbers by the April 1, 2001, 
statutory deadline.
The Census 2000 Dress Rehearsal
    In preparing for Census 2000, the Census Bureau, as has been its 
practice for many decades, conducted a dress rehearsal, or full-scale 
census simulation, in several sites across the country.\16\ The dress 
rehearsal demonstrated the operational feasibility of producing the 
statistically corrected block-level data by the statutory deadline. The 
Census Bureau was able to produce data without the use of statistical 
sampling within nine months (as it is required to do for apportionment) 
and statistically corrected data within 12 months (as it is required to 
do for redistricting).
---------------------------------------------------------------------------

    \16\ Sacramento, California; Menominee County, Wisconsin; and 
Columbia, South Carolina and 11 surrounding counties.
---------------------------------------------------------------------------

Technical Feasibility

    Technical feasibility refers to whether the statistical methodology 
used by the A.C.E. will improve accuracy. Measuring the accuracy of the 
census is not a simple task. There are two types of accuracy--numeric 
and distributive--central to census operations and the uses of census 
data. Starting with the planning for the 1980 census, the Census Bureau 
has developed, tested, refined, and implemented statistical methods to 
improve both the numeric and distributive accuracy of the census 
enumeration, culminating in the 2000 A.C.E. design. The Census Bureau 
expects the A.C.E. to improve both numeric and distributive accuracy.
Defining Numeric and Distributive Accuracy
    In analyzing the effect of the A.C.E. on accuracy, this discussion 
focuses on the accuracy of population totals for geographic areas and 
demographic groups, and, though important in the overall understanding 
of the census, not on the accuracy of detailed characteristic data for 
people or housing units.
    Numeric accuracy refers to how close the overall count of a 
particular geographic area or demographic group is to the ``truth,'' 
that is, to the actual number of people who reside in that area or 
belong to that group. Distributive accuracy refers to how close the 
relative proportion or share of a geographic area or demographic group 
is to its true share relative to other areas or groups. A census 
operation that increases numeric accuracy moves the overall count for 
any particular area or demographic group closer to the true total. For 
example, an operation that enumerates individuals in a particular state 
who would otherwise be missed, increases the numeric accuracy of that 
state. A census operation that increases distributive accuracy will 
improve the accuracy of the population share for a given area or 
demographic group compared to other areas or demographic groups `` in 
other words, improve the accuracy of the estimated proportions or 
shares of the total population for the areas or groups.
    A perfect census--one in which every resident is counted once and 
only once and is correctly located--would be both numerically and 
distributively accurate. But, as noted above, the Census Bureau's 
experience leads it to expect that, absent statistical correction, 
Census 2000 will result in both a net national undercount and various 
differential undercounts. Such undercounts affect both numeric and 
distributive accuracy. Although much of the analysis of the 1990 census 
focused on distributive accuracy, both types of accuracy are important 
and must be considered in designing a census that

[[Page 38381]]

will provide the most accurate count possible.
Importance of and Relationship Between the Two Types of Accuracy
    The decennial census can be viewed as one of the nation's most 
important civic ceremonies. Viewed in this broad perspective, securing 
maximum participation must be a key Census Bureau goal. To the extent 
that the census has the obligation to fully reflect who Americans are 
and how they live, everyone should be counted. Census operations that 
improve numeric accuracy, irrespective of their impact on distributive 
accuracy, meet this most basic goal.
    In contrast, census operations that improved distributive accuracy 
but left many residents out of the count would not meet this basic 
goal. For example, a census that counted 90 percent of every 
demographic group in every geographic area would be distributively 
accurate, but would fail the obligation of the census to include 
everyone.
    Numeric accuracy of census data is particularly important when 
population thresholds determine eligibility for program funding. For 
example, in FY 1998, the U.S. Department of Housing and Urban 
Development obligated over $3 billion under its Community Development 
Block Grants Entitlement Program. For this program, the population 
thresholds used are central cities of metropolitan statistical areas; 
other cities over 50,000 in metropolitan statistical areas; and 
qualified urban counties of at least 200,000 (excluding the population 
in entitlement cities located within the boundaries of such counties). 
Central city and metropolitan statistical area designations themselves 
depend upon certain population thresholds.
    Additional uses of census data for which numeric accuracy is 
critical are associated with the Census Bureau's intercensal population 
estimates and survey controls. Decennial census data are the base for 
the Census Bureau's intercensal population estimates and projections 
programs, programs that produce annual population estimates for all 
general purpose governments and projections for the nation and states, 
respectively. Specific uses of the population estimates that depend on 
numeric accuracy include use of the estimates as controls for many 
federal surveys, including the Current Population Survey (which 
provides monthly labor force and employment data), and as denominators 
for many critical federal data series, such as birth, mortality, and 
cancer rates, as well as per capita income.
    For the purpose of reapportioning seats in the House of 
Representatives, distributive accuracy becomes a principal concern, 
because reapportionment is based on a proportionate allocation formula. 
Federal and state redistricting are based on criteria for dividing 
state populations into districts of equal size; thus both numeric and 
distributive accuracy are important. Distributive accuracy is also 
central to federal funding allocations that distribute funds based on 
relative percentage of the population.
    The goal of the Census Bureau is to conduct a census that is both 
numerically and distributively accurate. This said, it is numeric 
accuracy that drives the process for designing Census 2000 operations 
other than the A.C.E. When it designs a decennial census, the Census 
Bureau has available a very large number of possible operations. It 
assesses these operations against such criteria as cost, statutory 
deadlines, whether the staff necessary to implement these operations 
can be recruited and adequately trained, and how well the operations 
fit with other operations under consideration. In this extensive 
process of evaluating individual operations and then assembling them in 
the final design, there is one paramount criterion: what census design 
has the highest probability of correctly enumerating the population? 
That is, can an operation considered separately, and when combined with 
other operations, be expected to help the Census Bureau correctly count 
as many people as possible, given funding, timing, and other 
constraints?
    Obviously, if perfect numeric accuracy were achieved for all 
geographic areas and demographic groups, then perfect distributive 
accuracy would also result. However, because it is difficult and 
perhaps impossible to know a priori the effects of a particular census 
operation on distributive accuracy, assessing an operation's effect on 
distributive accuracy can rarely be part of the planning process. The 
difficulty of designing operations for distributive accuracy is 
compounded if it is to be achieved across geographic areas and multiple 
demographic groups and then simultaneously across many levels of 
geography. For example, the Local Update of Census Addresses program, 
being voluntary, may have benefitted communities with strong local 
planning departments more than other communities. This program, then, 
had an unpredictable effect on distributive accuracy.
    In principle, any given census operation designed to increase 
numeric accuracy can increase distributive accuracy, leave it the same, 
or make it worse. But in assembling a census design, the Census Bureau 
does not reject operations that would improve numeric accuracy (and 
meet other criteria for inclusion) even though such operations might 
affect distributive accuracy negatively, or indeterminately. For 
example, the Census Bureau has developed for Census 2000 an extensive 
partnership program to assist local jurisdictions and community 
organizations in promoting participation in the census. But increasing 
the counts for these participating localities will not necessarily 
translate into improvements in distributive accuracy. If one state 
promotes the census more effectively than another state, the state with 
the better promotion program may earn a higher share of the total 
national population than would otherwise be the case.
    Although the Census Bureau has largely targeted its coverage 
improvement programs in the areas that have been the most difficult to 
count, it has not rejected census operations that might 
disproportionately improve the count for groups that are already well 
counted. An example of the latter in Census 2000 is the ``New 
Construction'' program.\17\ Moreover, the Census Bureau has supported 
the efforts of neighborhoods, cities, and states to increase the 
accuracy of their census counts, irrespective of the effect on 
distributive accuracy. The Census Bureau views these increases in 
numeric accuracy, even for well counted groups, as important to the 
most basic goal of the census--counting everyone.
---------------------------------------------------------------------------

    \17\ In this program, local and tribal governments liaisons in 
mailout/mailback areas review the Census Bureau's address list for 
their areas and provide the agency with the addresses of all newly 
constructed housing units as of April 1, 2000. The Census Bureau 
matches these addresses to its address list, updated with United 
States Postal Service files, and verifies and enumerates those 
addresses that are not on its address list.
---------------------------------------------------------------------------

    Finally, although different uses of census data depend to varying 
degrees on each type of accuracy, the two concepts are related. When 
the census falls short of overall numeric accuracy, states and 
localities with large populations that are differentially undercounted 
will suffer a diminution in proportionate shares. For example, the 
differential undercount in the 1990 census caused states and localities 
with large minority populations to suffer a diminution in share. The 
Census Bureau can and does try to improve both

[[Page 38382]]

numeric and distributive accuracy by bringing the total count for each 
area or demographic group closer to its true count.
Impact of the A.C.E. on Accuracy
    The preceding discussion of accuracy included a discussion of the 
design of the census for apportionment purposes, but did not consider 
the effects of the A.C.E. on numeric and distributive accuracy. As 
discussed below, the A.C.E. measures and corrects for the deficiencies 
in the initial census, and consequently the Census Bureau expects that 
the A.C.E. will improve both distributive and numeric accuracy.
    Based on decades of research identifying and measuring the 
undercount, as well as the 1990 census evaluations (discussed below), 
the Census Bureau expects the differential undercount to persist in 
Census 2000, with properties similar to those measured in 1990.\18\ 
This extensive research into measuring and correcting the differential 
undercount, augmented by enhancements to prior coverage measurement 
surveys, leads the Census Bureau to expect that the A.C.E. will improve 
accuracy. The A.C.E. is expected to improve numeric accuracy by moving 
total counts closer to the true count and to improve distributive 
accuracy by more accurately counting areas that contain significant 
populations of historically undercounted groups.
---------------------------------------------------------------------------

    \18\ This conclusion is based on the assumption that the 
coverage improvement programs used for Census 2000 will have similar 
results as those used in 1990.
---------------------------------------------------------------------------

    It is important to consider the contribution of the A.C.E. to 
numeric and distributive accuracy at different levels of geography. The 
Census Bureau expects that the A.C.E. will, on average, improve numeric 
accuracy for geographic areas down to and including census tracts.\19\ 
``On average'' means that, while some tracts will be more numerically 
accurate using uncorrected numbers and others more accurate using 
corrected numbers, the average effect over all tracts is greater 
accuracy with than without the A.C.E. The Census Bureau also expects 
that improvement will be greatest for those areas that contain groups 
that have been historically undercounted.
---------------------------------------------------------------------------

    \19\ Bureau of the Census, ``Report to Congress--The Plan for 
Census 2000,'' 44-46. Census tracts are small, homogeneous, 
relatively permanent statistical subdivisions of counties formed for 
the purpose of collecting and tabulating decennial census data. 
Tracts typically contain between 1,000 and 8,000 people.
---------------------------------------------------------------------------

    Regarding distributive accuracy, the Census Bureau's extensive 
evaluations following the 1990 census led it to conclude that the 1990 
PES would have, on average, increased distributive accuracy for larger 
geographic areas, including states and cities and counties with more 
than 100,000 people. These evaluations did not determine whether the 
1990 PES would have improved the distributive accuracy of smaller 
geographic areas.\20\ In addition, these evaluations did not address 
whether the unadjusted counts were more accurate for these areas. The 
research on these issues conducted by the Census Bureau's Committee on 
Adjustment of Postcensal Estimates (CAPE) is discussed more fully 
below. Based on this research, the Census Bureau expects the 
incorporation of the A.C.E. results in the Census 2000 counts to have a 
similar effect, that is, to improve distributive accuracy for larger 
geographic areas, as in 1990.
---------------------------------------------------------------------------

    \20\ When apportionment is calculated based on Census 2000 
counts, the average Congressional District is expected to be over 
600,000 people.
---------------------------------------------------------------------------

Historical Experience With Coverage Measurement Surveys 
Demonstrates Feasibility

    The Census Bureau has a longstanding practice of employing 
scientific sampling techniques in the decennial census whenever 
sampling has the potential to lower costs without negatively affecting 
quality.\21\ It has devoted substantial resources for over two decades 
to the development of coverage measurement programs employing high 
quality sampling methodologies that enable the production of more 
accurate data. The feasibility assessment discussed in this document is 
one more logical step along that continuum.
---------------------------------------------------------------------------

    \21\ The Census Bureau first used sampling in a decennial census 
in 1940, in the program now known as ``long form'' enumeration, 
which is used to obtain detailed demographic information. The Census 
Bureau has used sampling to conduct federal surveys to collect key 
information, including unemployment and labor force data, etc., for 
many decades.
---------------------------------------------------------------------------

    The Census Bureau and leading professional statistical 
organizations have concluded that the best way to address the 
persistent problems of the undercount and the differential undercount 
is to complement traditional enumeration procedures with scientific 
sampling, using DSE. Extensive research, testing, and refinement of the 
tools of statistical adjustment have led the Census Bureau to determine 
that the A.C.E. will improve the overall accuracy of the census.
    The Census Bureau also has used Demographic Analysis to evaluate 
coverage in decennial censuses and broadly validate the coverage 
measurement survey results.\22\ Since independent Demographic Analysis 
estimates are not available below the national level, nor have 
estimates been available for detailed demographic groups (for example, 
tenure or detailed racial groups), the Demographic Analysis method has 
not been used to adjust the census for undercoverage.
---------------------------------------------------------------------------

    \22\ J.G. Robinson and others, ``Estimates of Population 
Coverage in the 1990 United States Census Based on Demographic 
Analysis,'' Journal of the American Statistical Association 88 
(September 1993): 1061-77.
---------------------------------------------------------------------------

The 1980 Census Experience

    Development of the modern coverage measurement survey began with 
the 1980 Post Enumeration Program, or PEP.\23\ The PEP was a coverage 
measurement survey, based on DSE methodologies, designed to evaluate 
the accuracy of the 1980 census. Over 50 lawsuits were filed regarding 
the 1980 census, most contending that the results of the PEP should 
have been used to adjust the census. However, the PEP had been designed 
primarily as a coverage evaluation tool, rather than an adjustment 
mechanism, making its use to correct the census results problematic. 
The Director of the Census decided not to adopt the numbers produced 
from this first attempt at statistical correction using DSE, judging 
the estimates to be flawed by missing and inaccurate data.\24\
---------------------------------------------------------------------------

    \23\ For a detailed discussion of the 1980 Census Post 
Enumeration Program, see Robert E. Fay and others, The Coverage of 
Population in the 1980 Census (Washington, D.C.: Government Printing 
Office, 1988), 37-92.
    \24\ Department of Commerce, ``Position on Adjustment of the 
1980 Census Counts for Underenumeration,'' Federal Register (16 
December 1980) vol. 45, no. 243, p. 82872.
---------------------------------------------------------------------------

    Significantly, however, the PEP operation provided a wealth of 
information on measuring coverage in a census using DSE. The PEP 
illustrated the potential use of coverage measurement surveys as a 
coverage evaluation tool for U.S. censuses. It was clear in principle 
that coverage measurement surveys could be used to correct the census. 
In the two subsequent decades, the Census Bureau built upon the 
knowledge and experience gained in the 1980 census.

Early Research and Development for the 1990 Census

    After the 1980 experience, the Census Bureau began an extensive 
review of its coverage measurement program to enhance the methods that 
had been used in 1980 and to determine the feasibility of a statistical 
adjustment in 1990. Adjustment of the census was a topic of lively 
debate in the statistical

[[Page 38383]]

community during the 1980s. Census Bureau professionals and outside 
statisticians published more than 100 papers on coverage measurement 
issues.\25\ In 1983, the Census Bureau formed the Undercount Research 
Staff, a staff of agency professionals charged with addressing coverage 
measurement issues and with assessing the potential correction of the 
1990 census. This group conducted research over the decade leading up 
to the 1990 census.
---------------------------------------------------------------------------

    \25\ See Tommy Wright and Joyce Farmer, ``A Bibliography of 
Selected Statistical Methods and Development Related to Census 
2000,'' 3rd ed., 1 May 2000, for a list of many of the most 
significant of these papers.
---------------------------------------------------------------------------

    Planning for the 1990 census progressed with a two-track approach--
preparing to take the best traditional enumeration possible, while 
simultaneously developing a Post-Enumeration Survey (PES), a coverage 
measurement survey the results of which could be used to statistically 
correct the census. The Census Bureau's position was that it would 
proceed with correction if it could determine, prior to the spring of 
1987, that implementation of a PES-based correction was feasible. As 
part of its research effort, the Census Bureau carried out the Test of 
Adjustment Related Operations (TARO) in 1986. Based on the results of 
the TARO, as well as various theoretical and empirical studies 
conducted since 1980, senior statisticians at the Census Bureau 
concluded that statistical methods existed that could produce census 
counts with a reduced differential undercount, and that if funded and 
successfully completed, the program incorporating these methods could 
be used to statistically correct the 1990 census.\26\
---------------------------------------------------------------------------

    \26\ Dan Childers and others, ``The Technical Feasibility of 
Correcting the 1990 Census,'' in Proceedings of the Social 
Statistics Section of the American Statistical Association Held in 
San Francisco, California, 17-20 August 1987.
---------------------------------------------------------------------------

    As discussed below, the Department of Commerce overruled the Census 
Bureau and decided not to allow adjustment of the 1990 census. The 
Census Bureau's research on the PES as a coverage measurement tool 
continued, including the conduct of the 1988 dress rehearsal Post-
Enumeration Survey. The 1988 dress rehearsal demonstrated significantly 
improved operations and once again demonstrated DSE's consistent 
ability to measure the undercount and the differential undercount.\27\
---------------------------------------------------------------------------

    \27\ Dan Childers and Howard Hogan, ``The 1988 Post Enumeration 
Survey Methods and Preliminary Results,'' in Proceedings of the 
Survey Research Methods Section of the American Statistical 
Association Held in New Orleans, Louisiana, 22-25 August 1988.
---------------------------------------------------------------------------

Litigation Challenging Decision to Halt 1990 Adjustment-Related 
Planning Activities

    The Department of Commerce, in the fall of 1987, directed the 
Census Bureau not to proceed with its plans to produce adjusted census 
figures, prompting the filing of a lawsuit against the Department and 
the Census Bureau. As part of that lawsuit, on July 17, 1989, the 
Department of Commerce entered into a stipulation, vacating the 
Department's 1987 decision against adjustment and requiring the 
Secretary to consider de novo, after the completion of the census, 
whether adjustment was warranted. The Census Bureau would conduct a PES 
and certain other adjustment-related planning operations, \28\ and the 
Secretary was to announce his decision on the adjustment issue by July 
15, 1991. Pursuant to the stipulation, the Department of Commerce 
agreed to develop and adopt promptly ``guidelines articulating what 
defendants believe are the relevant technical and nontechnical 
statistical and policy grounds for the decision on whether to adjust 
the 1990 Decennial Census population counts.'' An adjustment would be 
made if the Secretary of Commerce, in his judgment, determined that 
doing so would satisfy the guidelines. The stipulation also set up a 
Special Advisory Panel composed of four experts chosen by the 
plaintiffs and four experts chosen by the defendants; the Panel's role 
was to advise the Secretary regarding adjustment. At this time, the 
Census Bureau convened the Undercount Steering Committee, a group of 
senior career agency employees, and charged the committee with 
evaluating the conduct of the 1990 PES and assessing the accuracy of 
the adjusted versus the unadjusted census counts.
---------------------------------------------------------------------------

    \28\ Prior to the Department's 1987 decision halting the Census 
Bureau's adjustment-related planning activities for the 1990 census, 
the agency had planned to conduct a PES of 300,000 housing units. 
Under the terms of the stipulation, the Census Bureau agreed to 
conduct a PES of approximately 165,000 housing units, the results of 
which could be used to adjust the census.
---------------------------------------------------------------------------

    The Department of Commerce published its final guidelines on March 
15, 1990. \29\ The guidelines established, among other things, the 
principle that the unadjusted census counts would be presumed more 
accurate unless it could be shown that the adjusted counts were more 
accurate at the national, state, and local levels. This presumption and 
the guidelines in general will be discussed in greater detail below.
---------------------------------------------------------------------------

    \29\ Department of Commerce, ``Final Guidelines for Considering 
Whether or Not Statistical Adjustments of the 1990 Decennial Census 
of Population and Housing Should be Made for Coverage Deficiencies 
of the Population,'' Federal Register (15 March 1990) vol. 55, p. 
9838.
---------------------------------------------------------------------------

Conducting the 1990 Census and Deciding Against Adjustment

    The Census Bureau applied the DSE methodology in the 1990 PES to 
produce a second set of population counts for every block in the 
nation. \30\ Under the direction of the Undercount Steering Committee 
the Census Bureau analyzed the PES results extensively, producing 33 
separate and detailed technical reports analyzing various aspects of 
the survey and its results. The Census Bureau's extensive analysis was 
complemented by a large volume of outside expert analysis of the PES 
results. \31\
---------------------------------------------------------------------------

    \30\ Hogan, ``1990 Post-Enumeration Survey,'' 1054.
    \31\ Wright and Farmer, ``A Bibliography of Selected Statistical 
Methods Related to Census 2000.''
---------------------------------------------------------------------------

    Based on the Census Bureau's analyses, then Census Bureau Director 
Barbara Bryant and the majority of the Undercount Steering Committee 
recommended that the 1990 census be statistically adjusted. The Special 
Advisory Panel, convened as part of the stipulation, was divided in its 
recommendations regarding adjustment. The panel members selected by 
defendants all recommended against statistical adjustment, and the 
panel members selected by the plaintiffs all recommended in favor of 
adjustment. On July 15, 1991, Secretary Mosbacher announced that the 
1990 decennial census would not be statistically adjusted. \32\
---------------------------------------------------------------------------

    \32\ Department of Commerce, ``Adjustment of the 1990 Census for 
Overcounts and Undercounts of Population and Housing: Notice of 
Final Decision,'' Federal Register (22 July 1991) vol. 56, p. 33583.
---------------------------------------------------------------------------

    After the Secretary announced his decision, the plaintiffs returned 
to court, seeking an order compelling the Department to adjust the 1990 
census. On April 13, 1993, Judge McLaughlin of the U.S. District Court 
upheld Secretary Mosbacher's decision, determining that the decision 
was not arbitrary or capricious, although he stated that ``were this 
Court called upon to decide this issue de novo, I would probably have 
ordered the adjustment.'' \33\ Judge McLaughlin noted also that ``light 
of recent improvement in statistical tools and the practical benefits 
that the 1990 PES has provided, the use of adjustment in the next 
census is probably inevitable.'' \34\
---------------------------------------------------------------------------

    \33\ City of New York v. U.S. Dept. of Commerce, 822 F. Supp. 
906, 928 (E.D.N.Y. 1993).
    \34\ 822 F. Supp. 906 at 918, fn. 27.

---------------------------------------------------------------------------

[[Page 38384]]

Postcensal Estimates and Survey Controls Decision

    Although Secretary Mosbacher determined not to adjust the 1990 
census for estimated net census undercount, he deemed it appropriate 
that the Census Bureau consider using the adjusted counts as the basis 
for producing postcensal estimates: ``I am today requesting that the 
Census Bureau incorporate, as appropriate, information gleaned from the 
Post-Enumeration Survey into its intercensal estimates of the 
population.'' \35\
---------------------------------------------------------------------------

    \35\ Department of Commerce, ``Adjustment of the 1990 Census,'' 
33582.
---------------------------------------------------------------------------

    Census Bureau Director Bryant convened the Committee on Adjustment 
of Postcensal Estimates (CAPE) to study this issue and make 
recommendations to her. CAPE was a group of senior statisticians, 
demographers, and other Census Bureau professionals assembled to 
conduct additional analyses of the adjusted counts. The Committee's 
work extended over a 15-month period. The Committee issued a report on 
August 8, 1992, and an Addendum on November 24, 1992. \36\ The Addendum 
was the result of continuing and more focused analysis by the team. 
Taken together, the initial CAPE report and the Addendum found that the 
adjusted numbers were overall more accurate in terms of distributive 
accuracy at the state level and for areas with greater than 100,000 
population. For areas with populations of less than 100,000, the CAPE 
could not identify any improvement in distributive accuracy for the 
adjusted data. \37\
---------------------------------------------------------------------------

    \36\ CAPE; ``Additional Research on Accuracy of Adjusted Versus 
Unadjusted Census Base for Use in Intercensal Estimates,'' Addendum 
to Report of the Committee on Adjustment of Postcensal Estimates, 25 
November 1992, referred to later as CAPE Addendum.
    \37\ As will be discussed more fully below, more recent research 
has confirmed that the Census Bureau similarly cannot determine that 
the uncorrected 1990 data were more distributively accurate. For 
aggregations below 100,000, the evidence as to accuracy is 
indeterminate, that is, neither favoring the unadjusted nor the 
adjusted counts. See Bureau of the Census, ``Analysis of CAPE 
Findings on PES Accuracy at Various Geographic Levels,'' by Sally M. 
Obenski and Robert E. Fay, 9 June 2000.
---------------------------------------------------------------------------

    In January 1993, Dr. Bryant announced that the Census Bureau would 
not use the 1990 adjusted counts as the basis for producing postcensal 
estimates of the population. \38\ Director Bryant's Census decision was 
made in light of, though not explicitly governed by, the litigation 
guidelines that stated that adjustment was not warranted unless 
improvement could be clearly demonstrated down to small levels of 
geography, such as places and counties.
---------------------------------------------------------------------------

    \38\ Department of Commerce, ``Decision of the Director of the 
Bureau of the Census on Whether to Use Information from the 1990 
Post Enumeration Survey (PES) to Adjust the Base for the Intercensal 
Population Estimates Produced by the Bureau of the Census,'' Federal 
Register (4 January 1993) vol. 58, no. 1, 69.
---------------------------------------------------------------------------

    Recognizing the improvements in accuracy for certain uses of census 
data, Dr. Bryant decided to offer sponsors of federal sample surveys 
the option of having their surveys calibrated to population estimates 
benchmarked to adjusted census results. \39\ Accordingly, in December 
of 1993, the Bureau of Labor Statistics (BLS) requested that the Census 
Bureau convert the Current Population Survey controls to ones based on 
estimates incorporating the results of the 1990 PES. The BLS stated its 
conviction ``that the undercount-adjusted estimates provide a more 
accurate reflection of the level and distribution of the national 
population and that of most States than the estimates based on the raw 
Census counts.'' \40\ The BLS also requested that the population 
controls for the Consumer Expenditure Survey be adjusted in a similar 
fashion. \41\ Subsequent to the BLS decision, all other major national 
household surveys conducted by the Census Bureau for other agencies of 
the federal statistical system were converted to an adjusted population 
basis. Thus, corrected data from the 1990 census are already 
incorporated in many federal statistical series.
---------------------------------------------------------------------------

    \39\ Ibid., 70.
    \40\ Katharine G. Abraham, U. S. Bureau of Labor Statistics, to 
Harry A. Scarr, U. S. Bureau of the Census, 1 December 1993.
    \41\ Ibid.
---------------------------------------------------------------------------

Early Census 2000 Planning

    The results of the 1990 census led the Census Bureau, other 
professional statisticians, and Congress to conclude that significant 
changes were required for the next census. A comprehensive re-
examination of census methodology was needed to identify a census 
design that would improve the accuracy of the census. To this end, in 
November 1990, the Census Bureau established the ``Task Force for 
Planning for the Year 2000 Census and Census-Related Activities for 
2000-2009.'' The Task Force was responsible for defining a census 
design for Census 2000, considering both policy and technical issues, 
and a demographic measurement system for related activities for 2000 
through 2009.
    In June 1992, the General Accounting Office (GAO) released a 
comprehensive evaluation of the 1990 census, discussing lessons learned 
and identifying opportunities for fundamental, effective reforms. The 
GAO concluded that reduced data quality (including failure to make 
reductions in the net and differential undercounts)'' * * * is a cost 
of the current approach to taking the census * * *'' and that ``[t]he 
results from 1990 demonstrate that adding more resources [while 
employing traditional census-taking methods] is unlikely to allow the 
Bureau to enumerate that last remaining segment of the population.'' 
\42\
---------------------------------------------------------------------------

    \42\ General Accounting Office, Decennial Census: 1990 Results 
Show Need for Fundamental Reform, Report to Congressional 
Requesters, 9 June 1992, 62, 49 GAO/GGD-92-94.
---------------------------------------------------------------------------

    Also at the beginning of the decade, two panels of the National 
Academy of Sciences' (NAS) National Research Council were convened to 
study ways to improve the census for 2000. The Decennial Census 
Improvement Act of 1991, signed into law by President Bush, required 
the Census Bureau to contract with the National Academy of Sciences to 
study * * * the means by which the Government could achieve the most 
accurate population count possible * * *'' specifically considering, 
among other things, ''. . . the appropriateness of using sampling 
methods in combination with basic data-collection techniques or 
otherwise, in the acquisition or refinement of population data, 
including a review of the accuracy of data for different levels of 
geography * * *.'' \43\ The Panel on Census Requirements in the Year 
2000 and Beyond was established pursuant to this statutory requirement, 
supplementing the work already being performed by the NAS Panel to 
Evaluate Alternative Census Methods. This latter panel was established 
to provide an independent review of the technical and operational 
feasibility of the design alternatives and of the tests to be conducted 
by the Census Bureau. The Methods Panel's recommendations on testing 
and design alternatives informed the final design of the original plan 
for Census 2000. The Panel issued its final report in 1994, 
recommending that the agency use sampling as an essential part of 
census-taking in Census 2000. \44\
---------------------------------------------------------------------------

    \43\ Congress, House, Decennial Census Improvement Act of 1991, 
102nd Cong., 2nd sess., H.R. 3280, Congressional Record, daily ed. 
(9 October 1991), H7694 became Public Law 102-135 on October 24, 
1991. It was set forth in the commentary to Title 13, U.S. Code, 
sec. 141.
    \44\ Duane L. Steffey and Norman A. Bradburn, Counting People in 
the Information Age (Washington, D.C.: National Academy Press, 
1994), 4.
---------------------------------------------------------------------------

    In June 1995, the Task Force convened at the beginning of the 
decade issued final recommendations in its ``Global Report,'' 
suggesting a number of

[[Page 38385]]

improvements for Census 2000. \45\ The Task Force endorsed the Census 
Bureau's basic plan to conduct an Integrated Coverage Measurement (ICM) 
survey and suggested that the Census Bureau pursue an ICM design that 
would incorporate the best features of alternative methodologies, 
including DSE and CensusPlus. \46\ The Census Bureau tested these 
alternate methodologies in the 1995 Census Test, concluding along with 
the NAS Panel to Evaluate Alternative Census Methodologies that DSE 
offered the best opportunity to produce high quality statistical 
correction. \47\
---------------------------------------------------------------------------

    \45\ Bureau of the Census, ``Reinventing the Census,'' Global 
Report of the Task Force for Planning the Year 2000 Census, June 
1995.
    \46\ For a description of these methodologies and the 
differences between them, see White and Rust, Preparing for the 2000 
Census: Interim Report II, 48-51.
    \47\ A third National Academy of Sciences panel, the Panel to 
Evaluate Alternative Census Methodologies, was convened to study 
ways to improve the census for 2000. In its earlier report (Andrew 
A. White and Keith F. Rust, eds., Sampling in the 2000 Census: 
Interim Report I (Washington, D.C.: National Academy Press, 1996) 
following the 1995 Census Test, but before all the analyses from 
that test had been completed, the Panel concluded that ''* * * 
nothing in the [1995] census test, nor any other development, 
suggests that a decennial census that * * * reduces differential 
undercoverage can be conducted without the use of some form . . . of 
sampling for integrated coverage measurement'' (pp. 2-3). Based on 
the performance of DSE versus CensusPlus in the 1995 Census Test, 
the Census Bureau selected the former methodology for Census 2000, 
and the Panel supported that decision (White and Rust, Preparing for 
the 2000 Census: Interim Report II, 51-59).
---------------------------------------------------------------------------

    Also in that year, the Panel on Census Requirements in the Year 
2000 and Beyond issued its final report. The Panel recommended the use 
of sampling and estimation techniques in Census 2000, concluding that:

    It is fruitless to continue trying to count every last person 
with traditional census methods of physical enumeration * * *. It is 
possible to improve the accuracy of the census count with respect to 
its most important attributes by supplementing a reduced intensity 
of traditional enumeration with statistical estimates of the number 
and characteristics of those not directly enumerated.\48\
---------------------------------------------------------------------------

    \48\ Edmonston and Schultze, Modernizing the U.S. Census, 3.

The Census 2000 Dress Rehearsal

    The Census Bureau conducted a dress rehearsal in 1998 in several 
sites across the country, an important opportunity to test the DSE 
methodology in as near a census-like environment as possible. The 
Census Bureau concluded from the dress rehearsal results that ``[t]he 
data showed across-the-board that the undercount, which has been 
measured in every census since 1940, persists today, but that 
scientific methods used at two of the three test sites corrected for 
it.'' \49\ The dress rehearsal data also displayed the persistence of 
the differential undercount.\50\ In Sacramento, the estimated 
undercount rates that would have resulted without the use of Integrated 
Coverage Measurement were 4.7 percent for non-Hispanic Whites, compared 
to 8.7 percent for African Americans, 8.3 percent for Hispanics, and 
6.0 percent for Asians. In Menominee County, Wisconsin, which is 
largely composed of the Menominee American Indian Reservation, the 
estimated undercount rate for non-Hispanic American Indians that would 
have resulted without the use of Integrated Coverage Measurement was 
4.1 percent. In the South Carolina site, the estimated undercount rate 
for non-Hispanic Whites was 6.3 percent and 13.2 percent for all others 
(Hispanic, Black, American Indian, Hawaiian, and Asian).
---------------------------------------------------------------------------

    \49\ Department of Commerce, ``Census 2000 Dress Rehearsal Shows 
Undercount Persists; Scientific Methods Correct Race and Ethnic 
Differential,'' Commerce News, 20 April 1999, CB99-CN.16 (revised).
    \50\ Bureau of the Census, ``Some Results from the Census 2000 
Dress Rehearsal,'' by Rajendra Singh, DSSD Census 2000 Dress 
Rehearsal Memorandum Series A-76, 26 February 1999, 6.
---------------------------------------------------------------------------

    It is clear from these results that, based on traditional census-
taking methods alone, there was a substantial net undercount in all 
three sites, as well as a differential undercount of racial and ethnic 
minorities in those jurisdictions. The dress rehearsal demonstrated the 
operational feasibility of the A.C.E. and enhanced the Census Bureau's 
knowledge of the properties of statistical correction.

External Review

    The Census Bureau's confidence that the application of the DSE 
methodology will result in a more accurate census is shared by many 
other entities that have critically examined this issue. Four different 
NAS panels over the decade have clearly endorsed the concept that a 
properly designed and executed coverage measurement survey has the 
potential to produce a more accurate census.\51\ In 1999, the NAS Panel 
to Evaluate Alternative Census Methodologies concluded that:
---------------------------------------------------------------------------

    \51\ A fourth NAS panel was convened in June 1998 to review the 
Census Bureau's plans, procedures, and operations in connection with 
the Dress Rehearal and Census 2000. Experts from this panel are 
examining, among other things, the statistical methodology and 
procedures for the A.C.E.

    The only cost-effective methodology available for measuring the 
degree of differential undercoverage for subnational areas is a 
large-scale post-enumeration survey coupled with dual-system 
estimation * * *. If the Supreme Court prohibits use of integrated 
coverage measurement for apportionment, the panel still strongly 
supports a post-enumeration survey * * * for purposes other than 
apportionment.\52\
---------------------------------------------------------------------------

    \52\ Cohen, White, and Rust, Measuring a Changing Nation, 4.

    This recent conclusion is in line with those of the other three NAS 
panels. For example, in 1995, the Panel on Census Requirements in the 
Year 2000 and Beyond concluded that use of a high-quality survey in 
conjunction with the 2000 census will result in ``* * * improved 
accuracy with respect to the count and differential undercount for the 
nation as a whole as well as large areas and groups.'' \53\
---------------------------------------------------------------------------

    \53\ Edmonston and Schultze, Modernizing the U.S. Census, 100.
---------------------------------------------------------------------------

    Numerous other organizations agree that the use of a properly 
conducted scientific survey in conjunction with the enumeration has the 
potential to produce a more accurate census in 2000.\54\ These include, 
among others, the American Statistical Association, the American 
Sociological Association, the General Accounting Office, the Inspector 
General of the Department of Commerce, the Secretary of Commerce's 
Census 2000 Advisory Committee, the Census Bureau's Advisory Committee 
of Professional Associations, and the Census Bureau's Race and Ethnic 
Advisory Committees.\55\
---------------------------------------------------------------------------

    \54\ While support is widespread, the Census Bureau does not 
mean to imply that there is unanimous support on the issue. See, for 
example, Lawrence D. Brown and others, ``Statistical Controversies 
in Census 2000,'' Jurimetrics 39 (Summer 1999).
    \55\ Bureau of the Census, ``Report to Congress--The Plan for 
Census 2000,'' 24-25; Joint Census Advisory Committees on the Racial 
and Ethnic Populations, ``Recommendations Agreed Upon by the Four 
Census Advisory Committees on the African American, American Indian 
and Alaska Native, Asian and Pacific Islander and Hispanic 
Populations Made at the Meeting Held on May 22-23, 1997,'' 
Recommendation 3; the Secretary of Commerce's 2000 Census Advisory 
Committee, ``Final Report, Recommendation 3B, Post Enumeration 
Survey with a Traditional Census,'' 22 January 1999; and Census 
Advisory Committee of Professional Associations, ``Recommendations 
Made as a Result of the Meeting on April 22-23, 1999,'' 
Recommendation 1.
---------------------------------------------------------------------------

A.C.E. Implementation Issues

    The 1990 census coverage measurement survey was one of the most 
thoroughly evaluated programs conducted by the Census Bureau. The 
Census Bureau and other interested parties have analyzed volumes of 
data on the survey's effects on accuracy and how its results compared 
to the 1990 unadjusted census. Some of this analysis was performed in 
conjunction with Secretary Mosbacher's 1991 decision and the 1992 
Committee on

[[Page 38386]]

Adjustment of Postcensal Estimates (CAPE) report, but the Census Bureau 
has continued to examine the adjusted and unadjusted census data from 
1990. These analyses have further clarified the relationship between 
the adjusted and the unadjusted 1990 census counts.
    The extensive study of the 1990 coverage measurement survey 
identified a number of issues. The Census Bureau has considered these 
and other issues in assessing the feasibility of statistically 
correcting the Census 2000 counts. The following discussion presents 
many of these issues and addresses why the Census Bureau expects the 
A.C.E. to improve the overall accuracy of the census. In addition, 
changes in the A.C.E. design and their impact on accuracy are 
discussed.

Measuring Accuracy

    Measuring accuracy in both the enumeration and the coverage 
measurement survey involves examining two types of error. One type, 
sampling error or variance, arises from the use of a sample to 
represent a population. Sampling error will occur only in the A.C.E. 
The other type, often termed nonsampling error, represents all other 
sources of error. Of particular concern in nonsampling errors are 
systematic errors or biases. Nonsampling errors will occur in both the 
initial census and the A.C.E. The most serious source of bias in the 
initial census is coverage error resulting from people missed or 
erroneous enumerations. The most notable example of bias in the 
enumeration is the historical phenomenon of the net undercount, 
including the differential undercount. Bias can also occur in the 
A.C.E., including errors due to false matches or nonmatches, 
inaccurately accounting for missing information, and other systematic 
collection or processing errors.
    In designing coverage measurement surveys, the Census Bureau must 
strike a balance between sampling variance and bias. In comparing the 
accuracy of the 1990 coverage measurement survey to the accuracy of the 
unadjusted census, the Census Bureau concluded that the combined error 
in the coverage measurement survey was lower than the large bias in the 
census enumeration and therefore recommended adjustment. Secretary 
Mosbacher did not accept this recommendation and explained his reasons 
for not adjusting in his 1991 decision paper.

Assessment of Issues Emerging from 1990

    The scrutiny and analysis of the 1990 census adjustment decision 
extended and sharpened discussions in the statistical community 
regarding the use of a coverage measurement survey to correct for 
census undercounts. Many of these issues were the subject of extensive 
discussion in Secretary Mosbacher's July 1991 decision document and in 
the 1992 CAPE report. Over the past decade, issues regarding the use of 
sampling to correct the census have been debated frequently in the 
technical literature.\56\
---------------------------------------------------------------------------

    \56\ Wright and Farmer, ``A Bibliography of Selected Statistical 
Methods Related to Census 2000.''
---------------------------------------------------------------------------

    Some of these issues primarily address the basic principles and 
theories that must be considered in determining the proper application 
of a coverage measurement survey and DSE. For these issues reasoned 
judgment has to be invoked, and it is difficult to resolve these issues 
definitively by quantitative measurements. For example, what is the 
proper standard for deciding whether the coverage measurement survey 
should be used to correct the census? What priority should be given to 
numeric versus distributive accuracy? What are plausible assumptions 
about the distribution of individuals who are missed by both the 
initial census and the coverage measurement survey?
    Other issues focus more on how well the Census Bureau can implement 
the coverage measurement survey, including the estimation processes. Is 
it operationally feasible to conduct the A.C.E. and produce the 
corrected results within the decennial time frame? Are the levels of 
sampling variance associated with the A.C.E. estimates reasonable? Can 
the levels of matching or other processing errors that occur in A.C.E. 
operations be kept to a minimum? These issues, while still subject to 
some degree of technical judgement, can often be evaluated by an 
examination of quantitative data.
    As part of its comprehensive assessment of the A.C.E. design, 
senior Census Bureau officials requested a careful analysis of the 
technical issues identified in both the Mosbacher document and the CAPE 
report in order to ensure that cited concerns about accuracy had been 
adequately addressed. The Census Bureau's analysis of the Mosbacher 
document focused on the Secretary's guidelines and on supporting 
evidence for his decision.\57\ The Census Bureau's analyses of the CAPE 
report focused on the accuracy of the unadjusted versus the adjusted 
census counts for different levels of geography and the status of the 
technical issues introduced.\58\
---------------------------------------------------------------------------

    \57\ Bureau of the Census, ``An Analysis of the Consistency of 
the 1990 Mosbacher Guidelines to U.S. Census Bureau Standards,'' by 
Sally M. Obenski and Robert E. Fay, 16 May 2000.
    \58\ Obenski and Fay, ``Analysis of CAPE Findings on PES 
Accuracy''; and Bureau of the Census, ``Analysis of CAPE Findings on 
1990 PES Technical Issues,'' by Sally M. Obenski, 9 June 2000.
---------------------------------------------------------------------------

    In addition to the discussion of technical issues, Secretary 
Mosbacher's analysis (and other reports critical of sampling) 
introduced a number of non-technical considerations. Secretary 
Mosbacher, for example, opined that ``adjustment would open the door to 
political tampering with the census in the future'' \59\--a theme 
frequently repeated in political, though not in scientific, discussions 
of sampling. No evidence has been presented that the Census Bureau has 
the competence to assess how its selection or implementation of census 
operations, including the many technical components of the A.C.E., 
might predetermine partisan outcomes. Furthermore, the highly pre-
specified A.C.E. procedures make Census 2000 highly resistant to any 
form of manipulation. Although there are a number of agencies and 
groups--including the congressional committees charged with oversight 
of Census 2000, the General Accounting Office, the Census Monitoring 
Board, the Inspector General of the Department of Commerce, numerous 
advisory committees and other watchdog efforts--scrutinizing the 
planning and conduct of Census 2000, no evidence has been presented 
suggesting that the Census Bureau has any intention to affect political 
outcomes, or, if it did, that it has the technical ability to do so. 
The Census Bureau disputes any and all accusations that it would act 
out of political motives, and in this document restricts its discussion 
of concerns about the A.C.E. to those with technical and scientific 
content.
---------------------------------------------------------------------------

    \59\ Department of Commerce, ``Adjustment of the 1990 Census,'' 
33583.
---------------------------------------------------------------------------

The Proper Standard To Use in Deciding Whether to Statistically Correct 
the Counts for Non-Apportionment Purposes

    As was discussed earlier, Secretary Mosbacher's adjustment decision 
regarding the 1990 census was controlled by eight guidelines 
promulgated in connection with pending litigation. Secretary 
Mosbacher's decision not to adjust the 1990 census was based in large 
part on the standard articulated in the first guideline--that the 
unadjusted census would be ``* * * considered the most accurate count 
of the population of the United States, at the national, state, and

[[Page 38387]]

local level, unless an adjusted count is shown to be more accurate.''
Analysis and Response
    This guideline assumed a priori that the unadjusted census counts 
were superior and required proof that the adjusted counts were better 
in terms of distributive accuracy at all three levels. This decision 
guideline required the adjusted counts to satisfy criteria that no 
other census operation could meet--in effect, the 1990 census coverage 
measurement survey was subjected to a higher standard than all other 
census operations.
    If the Census Bureau had historically applied a similar presumption 
that a change to the census operation must demonstrate increased 
accuracy with convincing evidence for small levels of geography, it 
would not have made many important changes in census-taking 
methodology. For example, such a standard would not have permitted the 
Census Bureau to replace 100-percent in-home ``personal'' visits with 
mail questionnaires in the 1970 census. The Census Bureau did not know 
whether this fundamental change to the census operation would increase 
accuracy at all levels. Nor, in 2000, could the Census Bureau determine 
a priori that extensive promotion and paid advertising would increase 
accuracy at all levels, or for that matter, would be effective in all 
areas or for all demographic groups. If applied to all proposals to 
improve the initial census counts, this standard would effectively halt 
the Census Bureau's long tradition of scientific and technical 
innovation.
    For Census 2000, the Census Bureau will make the determination on 
whether to use the A.C.E. to correct Census 2000 after evaluating (1) 
the conduct of key operations, (2) the consistency of the A.C.E. 
results with historical measures of undercount, and (3) measures of 
quality. As described previously, the Census Bureau's comprehensive 
ongoing analyses and experience with conducting coverage measurement 
surveys have led it to expect that the A.C.E. will improve overall 
numeric and distributive accuracy and that it will reduce the 
differential undercount. Therefore, statistical correction is 
appropriate absent strong evidence that it will degrade the overall 
quality of the final census data. However, the Census Bureau will 
conduct an objective review before making a final determination to 
release the statistically corrected data. The process that the Census 
Bureau will follow in making this determination is described in more 
detail at the end of this document. The Census Bureau will be 
documenting and discussing both this process and the criteria on which 
the determination will be made in a public setting in the fall of 2000.

Numeric v. Distributive Accuracy

    The 1990 census adjustment decision (and the closely related 
decision on the adjustment of the postcensal estimates) was unequivocal 
in giving priority to distributive over numeric accuracy. Secretary 
Mosbacher interpreted the Constitutional and legal purposes of the 
census to require that:

* * * accuracy should be defined predominately in terms of getting 
the proportional distribution of the population right among 
geographic and political units. This argues for putting aside the 
judgment of accuracy based on getting absolute numbers right 
(numeric accuracy) and instead focusing on the question of whether 
there is convincing evidence that the accuracy of population 
distribution in the adjusted numbers (distributive accuracy) is 
superior to the distributive accuracy of the actual enumeration.\60\
---------------------------------------------------------------------------

    \60\ Ibid., 33593.

    This injunction, when joined with the standard in the first 
guideline, requires not only that the adjusted counts be demonstrably 
more accurate at very low levels of geography but that they be more 
distributively accurate at those levels. This emphasis was reflected in 
many of the technical papers that have been written on the 1990 census. 
Comparatively less attention has been directed to the importance of 
numeric accuracy, despite the importance that the Census Bureau 
attaches to it. In fact, Secretary Mosbacher critiqued the Census 
Bureau for its interpretation ``of accuracy as concerned with getting 
the number of people closer to the truth rather than getting the 
allocation of the population for the purposes of political 
representation and funding closer to the truth.'' \61\
---------------------------------------------------------------------------

    \61\ Ibid., 33592.
---------------------------------------------------------------------------

Analysis and Response
    The Census Bureau believes that the adjustment decision in 1990 did 
not adequately consider the improvements to numeric accuracy that can 
result from statistical correction. Numeric and distributive accuracy 
are discussed more fully above. The issue here is the relative 
importance that should be assigned to numeric and distributive accuracy 
in assessing the results of the coverage measurement survey. Judgments 
can differ on this issue. It is the strong judgment of the Census 
Bureau that in deciding whether to use a coverage measurement survey to 
improve the census, both numeric and distributive accuracy should be 
taken into account.
    The analysis and decision in 1990 focused almost exclusively on 
distributive accuracy. Although Secretary Mosbacher stated that the 
Census Bureau had provided substantial evidence (although ``not 
necessarily convincing'') that the adjusted counts were more 
numerically accurate, he based his conclusion not to adjust partially 
on the fact that improvements to distributive accuracy could not be 
demonstrated by convincing evidence at national, state, and local 
levels.\62\ Given the decision criteria introduced by Secretary 
Mosbacher, the CAPE also focused on distributive accuracy.
---------------------------------------------------------------------------

    \62\ Ibid., 33584.
---------------------------------------------------------------------------

    The interaction between numeric and distributive accuracy is quite 
complicated, but must be considered in the analysis of the two types of 
accuracy. Clearly, there are situations where gains in numeric accuracy 
are expected without improvement in distributive accuracy. For areas or 
groups that have similar undercount rates, improvements to numeric 
accuracy are expected from the A.C.E. corrections. However, the 
distributive accuracy of these areas will be unchanged by the 
correction, because they will experience similar corrections. This 
outcome is expected, because gains in distributive accuracy are 
realized when areas corrected for significant undercounts are compared 
with areas that have little undercount. Because the A.C.E. is designed 
to improve the numeric accuracy of areas with significant undercounts, 
the Census Bureau expects that the A.C.E. will improve both numeric and 
distributive accuracy and thus result in a more accurate census 
overall.

Correlation Bias

    Correlation bias is the result of either lack of independence 
between the initial census and the coverage measurement survey, or of 
variable inclusion probabilities within a post-stratum.\63\ Frequently, 
the term is used to refer to error caused by individuals systematically 
missed in both the initial census and the coverage measurement survey. 
Important assumptions for DSE are that everyone in a given post-stratum 
has a similar inclusion probability and that the census and the 
coverage measurement survey are independent. Technically, these 
assumptions are referred to as homogeneity and causal independence, 
respectively. Correlation bias occurs when these assumptions are not 
fully satisfied. Although it is theoretically possible for correlation 
bias to result in

[[Page 38388]]

either underestimation or overestimation by DSE, it is generally 
expected that correlation bias leads to underestimation. This will be 
the case, for example, when there are individuals who have little or no 
chance of being included in either the initial census or the coverage 
measurement survey. Some critics of the 1990 coverage measurement 
survey were concerned that correlation bias was so large as to preclude 
an improvement in distributive accuracy from adjustment.\64\
---------------------------------------------------------------------------

    \63\ CAPE, 21-23.
    \64\ Department of Commerce, ``Adjustment of the 1990 Census,'' 
33591-92.
---------------------------------------------------------------------------

Analysis and Response
    Correlation bias exists and will affect all dual system estimates. 
Post-stratification is used to minimize correlation bias. However, 
post-stratification is not a perfect solution, and it is reasonable to 
presume that some heterogeneity or causal dependence will persist, 
leading to some correlation bias. Comparisons with Demographic 
Analysis, though subject to limitations, have been used to obtain 
indications of possible correlation bias at the national level by age-
sex-race groups. These comparisons in 1990 suggested correlation bias 
for adult Black males, and gave much less or no evidence of correlation 
bias for other groups. These analyses were restricted to the national 
level, and gave no indication of how any persons reflected in 
correlation bias may have been distributed geographically. In fact, 
there are no empirical data that can be used to definitely measure 
correlation bias below the national level. As a result, different 
hypotheses have been set forth regarding whether the A.C.E. will 
improve accuracy, particularly distributive accuracy. In the absence of 
quantitative data, the issues regarding the effects of correlation bias 
can only be resolved by a review of the assumptions underlying the 
various hypotheses, and by making judgments regarding which assumptions 
are more plausible.
    The uncertainty about the geographic distribution of persons 
reflected in correlation bias relates to a concern of Secretary 
Mosbacher--the concern that because the distribution of those people 
missed by both the census and the coverage survey was not known, it 
could not be demonstrated that a statistical correction would improve 
distributive accuracy.\65\ However, such a concern implicitly assumes 
that the distribution of correlation bias in dual system estimates 
differs from the distribution of undercount, as estimated in A.C.E. 
While recognizing the inherent limitations of its knowledge about the 
distribution of correlation bias, the Census Bureau believes it is more 
plausible to assume that correlation bias will tend to be distributed 
in a positive relation to the distribution of estimated undercount 
rates. A range of models reflecting plausible assumptions for the 
distribution of correlation bias have been analyzed.\66\ This analysis 
of correlation bias, based on plausible assumptions, leads the Census 
Bureau to expect that improvements in distributive accuracy will be 
achieved by a properly designed and conducted coverage measurement 
survey.
---------------------------------------------------------------------------

    \65\ Ibid.
    \66\ William R. Bell, ``Using Information from Demographic 
Analysis in Post-Enumeration Survey Estimation,'' Journal of the 
American Statistical Association 88 (September 1993): 1106-1118; and 
Bureau of the Census, ``Report of the Working Group on the Use of 
Demographic Analysis in Census 2000,'' by William R. Bell and 
others, 6 May 1996.
---------------------------------------------------------------------------

    Potential effects of correlation bias on numeric accuracy can also 
be addressed. Correlation bias, when present, is generally expected to 
lead to underestimation by dual system estimates. Therefore, when the 
DSE estimates an undercount in the initial census, by implication the 
initial census counts are even more severely undercounted. So the 
statistical corrections based on DSE are moving the census counts in 
the right direction, though not far enough. Thus, the statistical 
correction improves numeric accuracy when the groups subject to 
correlation bias are also undercounted by the census. In fact, the 
group identified by Demographic Analysis as probably subject to 
significant correlation bias in 1990 `` adult Black males `` also had a 
high estimated undercount rate from the 1990 PES.\67\
---------------------------------------------------------------------------

    \67\ CAPE, Table 2, Attachment 3A.
---------------------------------------------------------------------------

    The Census Bureau expects that a properly designed and conducted 
coverage measurement survey should improve both numeric and 
distributive accuracy, even accepting that correlation bias cannot be 
eliminated. The Census Bureau will continue to use Demographic Analysis 
to assess the possibility of correlation bias at the national level.

Accuracy at Different Geographic Levels

    When Secretary Mosbacher decided not to use the adjusted data in 
1991, he indicated that the adjusted data could not be shown by 
convincing evidence to be more distributively accurate at the national, 
state, and local levels. The June 1991 Undercount Steering Committee 
report and later the August 1992 CAPE report concluded that adjustment, 
on average, improved distributive accuracy for states and areas with 
populations of more than 100,000.\68\ The CAPE report, however, left 
the erroneous impression that the unadjusted census was more accurate 
at small geographic areas, generally, areas with a population of fewer 
than 100,000.
---------------------------------------------------------------------------

    \68\ Bureau of the Census, ``Technical Assessment of the 
Accuracy of Unadjusted Versus Adjusted 1990 Census Counts,'' Report 
of the Undercount Steering Committee, 21 June 1991, p. 2; and CAPE, 
1.
---------------------------------------------------------------------------

Analysis and Response
    The CAPE report, issued on August 7, 1992, was followed by a 
November 25, 1992, Addendum. Because the CAPE work was conducted at the 
request of Secretary Mosbacher, the committee implicitly adopted the 
framework of the Mosbacher adjustment decision process in reaching its 
conclusions. That is, the adjusted census counts had to be shown to be 
more accurate at state and local levels in order to be adopted. The 
committee determined that it was unable to show that the adjusted 
census counts were more distributively accurate than the unadjusted 
counts for areas with fewer than 100,000 in population. Accordingly, 
the CAPE concluded that the unadjusted counts should be used in the 
postcensal estimates program. Unfortunately, the initial CAPE report 
could be interpreted as indicating that there was a problem with the 
accuracy of the adjusted census numbers for areas with a population of 
fewer than 100,000.
    It is important to understand, however, that the Census Bureau did 
not stop its research into small area accuracy with the initial CAPE 
report. The initial CAPE analysis reported the Census Bureau's results 
from its first comparisons, comparisons of similar areas. For example, 
areas with populations of fewer than 25,000 were compared to each 
other, and major metropolitan areas were compared to each other. But 
the Census Bureau conducted additional research, comparing large cities 
and counties to each other, to the balance of the nation, and to the 
balance of their respective states. This additional research reported 
in the Addendum documented additional evidence of improvements in 
distributive accuracy at sub-state levels.\69\
---------------------------------------------------------------------------

    \69\ CAPE Addendum.
---------------------------------------------------------------------------

    The correct interpretation of the CAPE report and the Addendum is 
that the Census Bureau could distinguish no improvement in distributive 
sub-state accuracy if the corrected numbers had been used to produce 
estimates for areas

[[Page 38389]]

with populations of less than 100,000. It is incorrect to infer that 
the unadjusted census produced more distributively accurate sub-state 
data. That question was not tested in the CAPE research.
    More recently, the Census Bureau has re-examined the CAPE data and 
determined that, based on available data, there is no basis for 
concluding that the unadjusted census was more distributively accurate 
than the adjusted counts for small areas.\70\ That is, in general, no 
differences in the distributive accuracy of these two sets of counts 
have been demonstrated for geographic areas with less than 100,000 
population.
---------------------------------------------------------------------------

    \70\ Obenski and Fay, ``Analysis of CAPE Findings on PES 
Accuracy.''
---------------------------------------------------------------------------

    Based on the CAPE and subsequent research and the expectation that 
the error structures of the initial census and A.C.E. operations for 
Census 2000 will be similar to 1990, the Census Bureau expects that the 
A.C.E. will, on average, increase distributive accuracy for areas with 
100,000 or more residents. For areas with fewer than 100,000 people, 
the predicted effect of the A.C.E. on distributive accuracy is 
indeterminate--neither favoring the initial census nor the corrected 
counts.
    With respect to numeric accuracy, as noted above, the Census Bureau 
expects that the A.C.E. will, on average, improve accuracy for 
geographic areas down to and including census tracts. Furthermore, the 
Census Bureau expects that improvement will be greatest for those areas 
that contain groups that have been historically undercounted.

Consistency with Demographic Analysis

    The analysis of the 1990 coverage measurement survey included a 
comparison of the adjusted census with estimates based on Demographic 
Analysis (DA).\71\ Discrepancies between the adjusted census and DA 
estimates led Secretary Mosbacher and others to question the accuracy 
of the 1990 adjusted census counts.
---------------------------------------------------------------------------

    \71\ Bell, ``Using Information from Demographic Analysis in 
Post-Enumeration Survey Estimation,'' 1106-1118; and Robinson and 
others, ``Estimates of Population Coverage in the 1990 United States 
Census,'' 1061-77.
---------------------------------------------------------------------------

Analysis and Response
    Demographic Analysis uses records and estimates of births, deaths, 
immigration, Medicare enrollments and estimates of emigration and 
undocumented immigration to estimate the national population, 
separately from the census. These demographic benchmarks are compared 
to the census counts, and the differences are used to create an 
estimate of the net census undercount. These estimates are produced for 
age groups (single years of age), sex, and broad race groups (Black, 
Non-Black). DA estimates can be used as independent benchmarks to 
validate the accuracy of coverage measurement survey estimates for 
corresponding demographic categories.
    It is important to note that DA, like coverage measurement surveys, 
has an associated level of uncertainty. The Census Bureau developed 
quantitative measures of uncertainty for the 1990 DA estimates, but 
these measures are based in part on professional judgment about the 
range of error in each of the underlying demographic components.
    How much uncertainty to assign to a DA estimate is therefore a 
matter of judgment. Different conclusions will be reached depending on 
basic assumptions about the accuracy of vital statistics and other 
records used in DA. In 1990, the Undercount Steering Committee 
concluded that the uncertainty in the DA estimates was of a magnitude 
that meant that many of the differences with the coverage measurement 
survey estimates resulted from random variation. However, Secretary 
Mosbacher reached another conclusion, citing several ``important and 
puzzling differences'' between the survey estimates and the DA 
estimates.\72\ The Census Bureau, based on previous work in this area, 
concluded that some noted differences were expected, but these 
differences did not call into question the results of the coverage 
measurement survey.\73\ Indeed, the difference between the DA and 1990 
PES estimates for adult Black males was beyond the bounds of 
uncertainty, demonstrating the utility of Demographic Analysis for 
assessing correlation bias at the national level. Other differences 
fell within acceptable bounds of uncertainty associated with both sets 
of estimates. The Census Bureau considered all differences between the 
DA estimates and coverage measurement survey estimates in its 
determination that the coverage measurement survey did improve the 
accuracy of the census counts. For Census 2000, the Census Bureau will 
continue to compare both the uncorrected and corrected census counts 
with DA estimates.
---------------------------------------------------------------------------

    \72\ Department of Commerce, ``Adjustment of the 1990 Census,'' 
33587.
    \73\ Bureau of the Census, ``Technical Assessment of the 
Accuracy of Unadjusted Versus Adjusted 1990 Census Counts,'' 4.
---------------------------------------------------------------------------

Timing

    In 1990, the adjusted data were not available for release until 
July 1991. This raises a concern about whether the Census Bureau can 
produce the statistically corrected data within the statutory deadline 
of April 1, 2001, for redistricting, without sacrificing the quality of 
the initial census or the A.C.E.
Analysis and Response
    The timing and quality of the initial census and the A.C.E. are 
related. The Census Bureau has developed a schedule for the initial 
census and for the A.C.E. operations that allows adequate time to 
produce uncorrected data for apportionment and corrected data prior to 
the statutory deadline. Barring some major, unanticipated operational 
difficulty,\74\ the Census Bureau expects to complete all data 
collection and processing functions for the initial census and the 
A.C.E. in time to deliver quality, statistically corrected 
redistricting numbers to the states prior to April 1, 2001.
---------------------------------------------------------------------------

    \74\ Census Bureau Director Dr. Prewitt provided examples of 
such operational difficulties in his February 14, 2000, letter to 
Chairman Dan Miller of the House Subcommittee on the Census. These 
examples include: (1) Problems with the payroll system that prevent 
the Census Bureau from paying its employees on a timely basis; (2) 
widespread problems filling enumerator positions, despite the 
agency's extensive pool of qualified applicants; and (3) problems 
with the Census 2000 address file that prevent Census Bureau 
employees from being able to fulfill their responsibilities.
---------------------------------------------------------------------------

    Critical differences between the 1990 census and plans for Census 
2000 should allow production of the corrected numbers within the 
required period. First, the 1990 plan was not premised on producing the 
adjusted numbers by the April 1 deadline. In fact, the 1990 litigation 
established a deadline of July 15, 1991, for delivery of the adjusted 
data.
    Second, there are improvements to the census that will make the 
initial Census 2000 operations more timely. While these improvements 
are directed at allowing enumeration data collection to occur closer to 
Census Day and therefore to be more accurate, they will also allow for 
an earlier start for the A.C.E. With respect to the key issue of 
staffing nonresponse followup so as to finish on schedule, which is 
crucial to the progress of both the census and the A.C.E., the Census 
Bureau has developed strategies to avoid the recruitment and retention 
problems that extended the 1990 census NRFU operation. The Census 
Bureau has conducted extensive research on how to ensure the 
recruitment and retention of well-qualified temporary employees. These 
strategies, successfully employed during the Census 2000 dress 
rehearsal, included the targeting of wage rates to local areas and a 
technique called frontloading. Frontloading is directed at

[[Page 38390]]

reducing the effects of early turnover of employees by hiring two 
employees for every position. As a result of these and other changes, 
nonresponse followup will take place in a shorter time period in Census 
2000. This shortening of nonresponse followup is in accord with the 
observations of the Census Bureau and the General Accounting Office 
that NRFU results decrease in accuracy as the time from Census Day 
increases.\75\ In addition, Census 2000 will not be repeating certain 
ineffective coverage improvement programs that delayed processing of 
the initial census in the 1990 coverage measurement survey.\76\
---------------------------------------------------------------------------

    \75\ Bureau of the Census, ``Characteristics of Census Errors,'' 
by Deborah Griffin and Christopher Moriarity, 1990 Decennial Census 
Preliminary Research and Evaluation Memorandum No. 179, 15 September 
1992; and General Accounting Office, Decennial Census--1990 Results, 
47.
    \76\ These coverage improvement programs are discussed briefly 
in Cohen, White, and Rust, Measuring a Changing Nation, 32-33.
---------------------------------------------------------------------------

    Third, several important changes will improve the timeliness of the 
A.C.E. operation. For example, the A.C.E. interviewers will have 
received more extensive training than in 1990. Additionally, the Census 
Bureau has developed a Computer Assisted Person Interviewing (CAPI) 
system for the A.C.E. that will allow enumerators to collect the data 
more quickly and accurately, and to transmit it electronically in a 
more expeditious manner by using laptop computers.
    In the unlikely event of an unanticipated, major operational 
difficulty, the Census Bureau will not curtail important operations key 
to the quality of the entire census to stay on schedule. For example, 
the Census Bureau will not curtail nonresponse followup in difficult-
to-enumerate neighborhoods to stay on the A.C.E. schedule. Likewise, 
the Census Bureau will not curtail the A.C.E. data collection 
activities. The Bureau is committed to achieving high quality in all 
census operations, and Census Bureau statisticians will be monitoring 
key A.C.E. performance information, such as response rates, for early 
warning about areas warranting corrective actions.

Level of Sampling Variance/Smoothing

    The levels of sampling variance and bias in the 1990 coverage 
measurement survey were important topics in the adjustment debate. 
Sampling variance is discussed in this section; bias will be discussed 
in the following section.
Analysis and Response
    One issue in 1990 was the use of a statistical technique called 
smoothing, a complex, model-based method designed to control sampling 
variance. The use of smoothing led to an extensive discussion regarding 
the robustness of the 1990 methodology. For Census 2000, the Census 
Bureau has developed the A.C.E. sample design so that smoothing will 
not be necessary. There were also concerns about the overall level of 
sampling variance in the 1990 coverage measurement survey.\77\ In 
developing the A.C.E. design, the Census Bureau thoroughly examined 
1990 variance issues and made important design decisions to reduce 
sampling variance levels. These include:
---------------------------------------------------------------------------

    \77\ Bureau of the Census, ``Adjustment of the 1990 Census,'' 
passim.
---------------------------------------------------------------------------

    <bullet> The A.C.E. sample size is almost double that of 1990, 
increased from approximately 165,000 to 314,000 housing units. Because 
sampling variance is inversely proportional to sample size, this 
increase will reduce the level of sampling variance in 2000.
    <bullet> The A.C.E. sample was designed to minimize the range in 
size of the sampling weights. Weights are assigned to categories of 
blocks (that is, small and large) that have different probabilities of 
being selected in the sample. When there is a wide range of weights, 
variance increases because blocks with large weights have a 
disproportionate effect on the variance of the estimates. The Census 
Bureau has designed its sampling procedures for Census 2000 
specifically to limit how much these weights will vary. This design 
will result in reduced sampling variance.\78\
---------------------------------------------------------------------------

    \78\ The NAS agrees that design changes in the A.C.E. will 
reduce the variance in block sampling weights, a ``key improvement 
in comparison to the 1990 design,'' May 3, 1999, letter from Janet 
L. Norwood, Chair, NAS Panel to Review the 2000 Census, to Kenneth 
Prewitt, Director, U.S. Bureau of the Census.
---------------------------------------------------------------------------

    The Census Bureau has used the 1990 experience to develop an 
enhanced A.C.E. sampling design, and does not anticipate that variance-
related issues will be a serious source of concern for the Census 2000 
coverage measurement survey.

Level of Nonsampling Error/Bias

    One concern was that the level of nonsampling error or bias in the 
1990 coverage measurement survey was so large that statistical 
correction would not result in an improvement in distributive 
accuracy.\79\ Critics of the A.C.E. have expressed similar concern 
about the anticipated level of bias in the Census 2000 DSE.\80\
---------------------------------------------------------------------------

    \79\ Bureau of the Census, ``Adjustment of the 1990 Census,'' 
and Leo Breiman, ``The 1991 Census Adjustment: Undercount or Bad 
Data?'' Statistical Science 9, no. 4 (1994): 458-537.
    \80\ David A. Freedman and Kenneth Wachter, University of 
California, letter to Rep. Miller, Chairman, House Subcommittee on 
the Census, 17 May 2000; and Brown and others, ``Statistical 
Controversies in Census 2000.''
---------------------------------------------------------------------------

Analysis and Response
    The Census Bureau conducted extensive evaluations of nonsampling 
error in the 1990 coverage measurement survey.\81\ These evaluations 
have given the Census Bureau a detailed understanding of nonsampling 
error. Based on this extensive work, the Census Bureau has concluded 
that the levels of nonsampling error in the 1990 PES did not prevent 
the statistical correction based on the coverage measurement survey 
from improving the accuracy of the census counts.\82\ The A.C.E. design 
includes enhancements to the 1990 coverage measurement survey that will 
even further control nonsampling error.
---------------------------------------------------------------------------

    \81\ Bureau of the Census, ``Technical Assessment of the 
Accuracy of 1990 Census Counts,''4; and Mary H. Mulry and Bruce D. 
Spencer, ``Accuracy of the 1990 Census and Undercount Adjustments,'' 
Journal of the American Statistical Association 88 (September 1993): 
1080.
    \82\ Bureau of the Census, ``Technical Assessment of the 
Accuracy of 1990 Census Counts,'' 1.
---------------------------------------------------------------------------

    It is important to note that some amount of bias in both the 
initial census and the A.C.E. is inevitable. However, the Census 
Bureau's analysis of bias, grounded in sound statistical principles, 
leads to the expectation that the improvements described in the 
following sections will control the levels of nonsampling error in the 
A.C.E. so that a statistical correction based on the A.C.E. will 
improve the uncorrected counts.

Enhancements to the Matching Process

    Matching refers to the determination of whether an individual 
enumerated in a coverage measurement survey is the same person as an 
individual enumerated in the initial census operation. Because errors 
in matching can significantly affect undercount estimates, highly 
accurate matching is an important component of the A.C.E. methodology. 
Although neither Secretary Mosbacher nor CAPE identified matching error 
as a significant problem with the 1990 coverage measurement survey, the 
Census Bureau has made significant improvements to the matching process 
in the 2000 A.C.E. design, and matching error is expected to be even 
lower in Census 2000 than in 1990:
    <bullet> A fully automated system supports computer and clerical 
matching, an advance over 1990 procedures that required handling and 
control of paper documents. This improvement provides for a number of 
built-in edits and quality checks to control matching error.

[[Page 38391]]

The automated matching system is the culmination of Census Bureau 
analyses and refinements over the last 20 years and will make searching 
and matching easier and more reliable.
    <bullet> The matching processes have been centralized in one site, 
rather than decentralized as in 1990, allowing for more effective 
control--a well-trained staff will perform all matching at a single 
location.
    <bullet> As discussed below, the change in the treatment of people 
who have moved since Census Day will simplify matching for these 
movers. Unlike in 1990, it will only be necessary to match people who 
resided in the sample blocks on April 1.

Enhancements to Computer Processing

    After the initial release of the adjusted numbers in July 1991, the 
Census Bureau discovered a computer processing error that resulted in a 
0.4 percent decrease in the estimated undercount for the 1990 census. 
The CAPE report reduced the Census Bureau's official undercount 
estimate from 2.1 percent to 1.6 percent, with 0.4 percentage points 
attributable to the computer processing error, and 0.1 percent 
attributable to additional processing corrections. Concerns have been 
raised relating to the Census Bureau's late discovery of the computer 
processing error. These concerns have been cited as evidence that the 
complexity of the computer operations associated with incorporating the 
results of a coverage measurement survey--like the A.C.E.--in the 
census counts makes the final numbers vulnerable to significant 
processing errors.\83\
---------------------------------------------------------------------------

    \83\ Congress, House, Committee on Government Reform and 
Oversight, Prepared Testimony of K.W. Wachter and D.A. Freeman 
Before the House Committee on Government Reform and Oversight, 104th 
Cong., 1st sess., 29 February 1996.
---------------------------------------------------------------------------

    The Census Bureau has adopted a number of methods to improve the 
quality of the A.C.E. software to guard against a similar error in 
Census 2000:
    <bullet> To ensure reliability, the Census Bureau has included 
software validation and verification strategies, such as independent 
software development of key computer programs (double programming).
    <bullet> To reduce ambiguity and increase communication, the Census 
Bureau has enforced standardized nomenclature and adopted an improved 
documentation approach for technical issues.
    <bullet> The Census Bureau has developed a Sample Design Control 
System. This system provided the necessary data to control, monitor, 
and validate the different phases of sampling. It also ensured that the 
software used to select the A.C.E. sample functioned correctly.
    <bullet> The software programs supporting the A.C.E. estimation 
process will be further validated by an Integrated Review System. This 
system will provide data on all phases of the estimation process that 
will allow timely validation that the software is performing as 
specified.
    These and other initiatives should result in a controlled, robust, 
and reliable A.C.E. computer processing environment. Therefore, the 
Census Bureau expects the processing for the Census 2000 A.C.E. to be 
not only more streamlined but also more reliable than it was for the 
1990 PES.

Enhancements to Minimize Missing Data

    Missing data cases involve the following situations where complete 
information cannot be obtained: missing characteristic data (race, age, 
or other characteristic information), complete non-interviews, or cases 
with insufficient information to determine an individual's enumeration 
or match status. In 1980, missing data in the coverage measurement 
survey was a serious problem and factored into senior statisticians' 
conclusion that the estimates were not sufficiently reliable to use for 
statistical adjustment of the census counts. The Census Bureau took 
steps to minimize missing data in the 1990 coverage measurement survey, 
and missing data in 1990 did not significantly affect the accuracy of 
the estimates.\84\ Nonetheless, concerns remain regarding the potential 
for high levels of missing data in the A.C.E.
---------------------------------------------------------------------------

    \84\ Bureau of the Census, ``Non-Response in Census Coverage 
Measurement Surveys and Its Impact--An Historical Review,'' by Ruth 
Ann Killion, DSSD Briefs, Information, and Topics Memorandum Series 
No. 44C, 17 September 1998, pp. 6-7.
---------------------------------------------------------------------------

    Building on its experience from the 1990 census, the Census Bureau 
has designed its field operations to minimize missing data. After the 
initial A.C.E. interview attempt, the Census Bureau will allow up to 
two additional weeks for attempts to revisit any nonresponding 
households. This two-week period of intense followup of nonresponding 
households will be conducted by the Census Bureau's best and most 
experienced available A.C.E. interviewers.\85\ Finally, Census Bureau 
staff will be monitoring missing data rates closely throughout the 
conduct of the A.C.E.
---------------------------------------------------------------------------

    \85\ This intensive field operation designed to minimize missing 
data is described in Childers and Fenstermaker, ``Accuracy and 
Coverage Evaluation: Overview of Design,'' 7.
---------------------------------------------------------------------------

    The Census Bureau has developed additional extensive procedures to 
deal with missing data. One method the Census Bureau uses to handle 
missing data in both the initial census and the A.C.E. is imputation. 
Imputation is an established statistical methodology that completes 
missing respondent information by incorporating information provided by 
other similar respondents. The imputation process for Census 2000 draws 
on lessons learned in the 1990 census. Additionally, the imputation 
process for Census 2000 has been simplified, which should result in the 
production of more easily validated data.
    While missing data were not a significant issue for the 1990 
census,\86\ some concerns have been expressed regarding the accuracy 
and robustness of the Census Bureau's imputation model for the 1990 
coverage measure survey.\87\ However, Census Bureau statisticians and 
others have conducted multiple evaluations using different 
methodologies to independently validate the imputation model used in 
the 1990 census.\88\ These evaluations and the improvements to missing 
data procedures discussed earlier lead the Census Bureau to expect that 
missing data will not be a substantial problem in the A.C.E.
---------------------------------------------------------------------------

    \86\ Secretary Mosbacher stated that levels of missing data were 
sufficiently low so that variation in the Census Bureau's missing 
data models made no difference in the outcome of the survey, and he 
concurred with the Undercount Steering Committee's judgment that the 
outcome was robust (Bureau of the Census, ``Adjustment of the 1990 
Census,'' 33600). The CAPE, accordingly, did not examine this issue.
    \87\ Brown and others, ``Statistical Controversies in Census 
2000.''
    \88\ T.R. Belin and others, ``Hierarchical Logistic-Regression 
Models for Imputation of Unresolved Enumeration Status in Undercount 
Estimation,'' Journal of the American Statistical Association 88 
(September 1993): 1149-66; and Bureau of the Census, ``Documentation 
of Handling Unresolved Enumeration Status in 1990 Census/Post-
Enumeration Survey,'' by Greg Diffendal and Tom Belin, STSD 
Decennial Census Memorandum Series V-98, 15 January 1991.
---------------------------------------------------------------------------

Homogeneity and the Synthetic Assumption

    Generally speaking, homogeneity refers to the principle that 
individuals grouped in a post-stratum have similar probabilities of 
being included in the census, that is, similar coverage probabilities. 
If homogeneity holds, conclusions can be drawn from a sample about 
population groups or geographic areas and the initial enumeration for 
these population groups or areas can be corrected with a coverage 
measurement survey. The synthetic assumption states that the people in 
a particular post-stratum are

[[Page 38392]]

relatively homogeneous and will generally share the same coverage 
factor. There are concerns, however, that a lack of homogeneity could 
lead to inaccuracies being introduced into the data for areas or 
population groups within the post-stratum.\89\
---------------------------------------------------------------------------

    \89\ K. Wachter and D. Freedman, ``Local Heterogeneity and 
Census Adjustment for the Intercensal Base,'' Technical Report No. 
381 (Berkeley, CA: University of California, Department of 
Statistics, 1993); and Brown and others, ``Statistical Controversies 
in Census 2000,'' 13.
---------------------------------------------------------------------------

Analysis and Response
    At issue is not whether there is perfect homogeneity; at issue is 
whether heterogeneity is too great to prevent an improvement from using 
the A.C.E. While the degree to which the homogeneity assumption holds 
is a continuing issue, the Census Bureau has made design improvements 
to the A.C.E. to control heterogeneity and believes that heterogeneity 
will not preclude the production of useful small area data in Census 
2000.
    The statistical correction that results from the A.C.E. is carried 
down to census blocks by applying the coverage correction factors 
within each A.C.E. post-stratum. The goal in constructing post-strata 
is to form groupings of the population that capture differences in the 
probabilities of being included in the census and the A.C.E.\90\ In 
effect, the inclusion probabilities are more similar for individuals 
within the same post-stratum than for individuals in different post-
strata. The coverage correction factors are calculated for each post-
stratum, based on a representative sample of the post-stratum, and thus 
reflect the net coverage of all people within the post-stratum. This is 
the underlying basis for applying this factor to the data records 
within the corresponding post-stratum to produce statistically 
corrected block totals which serve as the basis for Census 2000 
tabulations.
---------------------------------------------------------------------------

    \90\ This section presents a general discussion of the basis for 
synthetic or indirect estimation. There are more complex, but less 
stringent, requirements involving the relationship between census 
omissions and erroneous enumerations as discussed in Howard Hogan's 
paper, ``Accuracy and Coverage Evaluation: Theory and Application.''
---------------------------------------------------------------------------

    The more homogeneity within a post-strata and the more differences 
among post-strata, the greater the improvement from statistical 
correction. In designing post-strata, it is not necessary for each 
individual to have the same probability of inclusion. Since no two 
individuals are perfectly alike with respect to their chances of being 
included in either the initial census or the A.C.E., the goal for 
defining post-strata is to form groupings of the population with 
similar inclusion probabilities. That is, the goal is to form post-
strata that differentiate between groups of the population with respect 
to inclusion probabilities, and with respect to net coverage in the 
initial census. Some have suggested that an improvement will result 
from applying Demographic Analysis-based corrections within national 
post-strata consistent with DA.\91\ However, the Census Bureau expects 
to achieve greater improvements by having defined post-strata that take 
advantage of more local data.\92\
---------------------------------------------------------------------------

    \91\ David Freedman and Kenneth Wachter, ``Planning for the 
Census in the Year 2000,'' Evaluation Review, 20, (August 1996): 
355-77.
    \92\ Bureau of the Census, ``Accuracy and Coverage Evaluation 
Survey: Final Post-stratification Plan for Dual System Estimation,'' 
by Richard Griffin and Dawn Haines, DSSD Census 2000 Procedures and 
Operations Memorandum Series Chapter Q-24, 19 April 2000.
---------------------------------------------------------------------------

    The accuracy of the estimates that result from the application of 
the coverage correction factors depends on the degree to which the net 
coverage for areas or groups within a post-stratum is similar to the 
coverage correction factor that was developed for that post-stratum. 
The coverage correction factor is measured for the post-stratum based 
on a representative sample, and thus represents the net coverage for 
the post-stratum. Clearly, within the post-stratum, some degree of 
variation is expected from the measured coverage correction factor, and 
this variation will most likely be relatively greater for small areas. 
Thus, it is inevitable that the A.C.E. will result in the population in 
some blocks being overestimated and the population in other blocks 
being underestimated. The A.C.E. statistical correction was never 
intended nor expected to produce unqualified improvement in the 
smallest geographic areas, like blocks. That the A.C.E. does not 
produce improvement for every single block, however, is no reason to 
forego the benefits that will flow from the use of corrected census 
population counts at geographic levels of significance to data users. 
The Census Bureau expects that the A.C.E. estimates will produce better 
data for aggregations--such as states, congressional districts, 
counties, and cities--that are the basic areas for which census data 
are used.
    The Census 2000 A.C.E. incorporates improvements from the design 
used for the 1990 coverage measurement survey that are expected to 
improve the homogeneity within post-strata for Census 2000.\93\ The 
Census Bureau analyzed heterogeneity as part of the 1990 CAPE process, 
and has continued research for the A.C.E. post-strata.\94\ Building on 
the lessons learned from 1990, the Census Bureau has developed enhanced 
post-strata for Census 2000. For example, the A.C.E. post-strata 
definitions include mail return rate and type of enumeration 
variables.\95\
---------------------------------------------------------------------------

    \93\ Ibid.
    \94\ Robert E. Fay and John Thompson, ``The 1990 Post 
Enumeration Survey: Statistical Lessons in Hindsight,'' in 
Proceedings of the 1993 Annual Research Conference, 21-24 March 
1993.
    \95\ Griffin and Haines, ``Accuracy and Coverage Evaluation 
Survey: Final Post-stratification Plan for Dual System Estimation.''
---------------------------------------------------------------------------

    Some have cited the CAPE report as evidence that the Census Bureau 
had serious concerns about heterogeneity. A reading of the entire CAPE 
report, including the more technical Addendum, puts these concerns in 
proper perspective. That is, the full analysis of the CAPE report 
(including the Addendum) supports the expectation of the Census Bureau 
that the use of the A.C.E. results will lead to improvements in the 
accuracy of the Census 2000 data.

Additional Design Changes From 1990

    In addition to the specific improvements discussed previously, the 
Census Bureau has implemented other changes to the 1990 coverage 
measurement survey design. These changes, which will improve 
operational efficiency, include the use of the telephone in the A.C.E., 
and changes in the treatment of movers and the search area for 
matching. The Census Bureau will also collect data on race and 
ethnicity differently in Census 2000. The Census Bureau continues to 
consider and examine issues relating to these changes.

Use of the Telephone in A.C.E. Interviewing

    To gain efficiencies in the interviewing phase of the A.C.E., 
enumerators will conduct telephone interviews using CAPI laptop 
computers for households that have returned their census questionnaires 
by mail. By design, this interview will take place before or concurrent 
with the initial census nonresponse followup. The interviews will be 
conducted from the homes of the A.C.E. enumerators and will be 
conducted only for households that mail back a questionnaire that 
includes a telephone number. Furthermore, the households must be in 
areas where there is negligible risk of mail delivery problems--
generally, single family housing units or large multi-unit structures 
in areas with city-style mail delivery.
    The Census Bureau implemented this process to enhance the 
efficiency and

[[Page 38393]]

quality of the A.C.E. interview. Shortening the elapsed time from 
Census Day to the A.C.E. enumeration should improve data quality. Also, 
starting early in an environment that is more easily controlled should 
allow the A.C.E. enumerators to gain valuable experience in conducting 
interviews and in operating their laptop computers. The Census Bureau 
designed this process in a fashion that should maintain the 
independence between the A.C.E. and the other Census 2000 operations.

New Treatment to Account for Movers

    The Census Bureau has changed its treatment of individuals whose 
residence changes after Census Day. In the 1990 coverage measurement 
survey, movers were sampled where they lived at the time of the PES 
interview. The Census Bureau then searched the census records at the 
movers' April 1 usual residence to determine if they had been correctly 
enumerated in the census.\96\
---------------------------------------------------------------------------

    \96\ Hogan, ``Accuracy and Coverage Evaluation Theory and 
Application,'' 22.
---------------------------------------------------------------------------

    In the modified procedure employed by the A.C.E., the Census Bureau 
will combine information on movers from two sources to produce an 
estimate of movers who are missed in Census 2000. First, an estimate of 
the total number of movers will be calculated based on people who moved 
into the A.C.E. sample blocks between April 1 and the time of the 
A.C.E. interview. Second, the rate at which movers match to Census 2000 
will be based on reconstructing the Census Day residents of the A.C.E. 
sample housing units and matching these residents to the initial census 
records. Reconstructing the Census Day residents will be based on proxy 
interviews with the new residents or neighbors. These two estimates 
will be combined to form an estimate of the movers who are missed in 
Census 2000. These results are then used in the Dual System Estimation. 
The Census Bureau tested the modified procedure in the dress rehearsal 
and has judged this procedure to be the best blend of operational 
feasibility and accuracy.\97\
---------------------------------------------------------------------------

    \97\ Bureau of the Census, ``Minutes of the Executive Steering 
Committee on Accuracy and Coverage Evaluation Policy (ESCAP),'' 5 
January 2000.
---------------------------------------------------------------------------

Search Area for Matching

    The Census Bureau's search operation in the 1990 coverage 
measurement survey used an extended search area in blocks adjacent to 
the sample blocks.\98\ The extended search area included one ring of 
adjacent blocks, or two rings of adjacent blocks in most rural areas. A 
person located in either the sample or an adjacent block was labeled a 
correct enumeration or match. Defining the search area in this fashion 
provided significant gains in reducing sampling variance. For Census 
2000, the A.C.E. search area has been designed to achieve the gains in 
controlling sampling variance, while providing operational 
efficiencies.
---------------------------------------------------------------------------

    \98\ Hogan, ``1990 Post-Enumeration Survey,'' 1054.
---------------------------------------------------------------------------

    The Census 2000 search operation uses a sampling procedure that 
selects A.C.E. block clusters for an extended search. All block 
clusters are selected where there is evidence that an extended search 
will provide substantial information needed for the A.C.E. matching. 
Additionally, a random subsample of all other clusters is selected for 
the extended search.\99\ This decision was based on an analysis of the 
results of the 1990 census coverage measurement survey matching that 
indicated that this strategy would provide virtually the same gains in 
sampling variance reduction as compared to the 1990 results.\100\
---------------------------------------------------------------------------

    \99\ Childers and Fenstermaker, ``Accuracy and Coverage 
Evaluation: Overview,'' 8-9; and Bureau of the Census, ``Accuracy 
and Coverage Evaluation: The Design Document,'' by Danny R. 
Childers, DSSD Census 2000 Procedures and Operations Memorandum 
Series Chapter S-DT-01.
    \100\ Bureau of the Census, ``Accuracy and Coverage Evaluation 
Survey: Targeted Extended Search Plans,'' by Alfredo Navarro, DSSD 
Census 2000 Procedures and Operations Memorandum Series #Q-18, 12 
January 2000.
---------------------------------------------------------------------------

Reporting More Than One Race

    In accordance with direction from the Office of Management and 
Budget,\101\ Census 2000 will for the first time allow individuals to 
report more than one racial category. This guidance from the OMB 
necessitates that the A.C.E. post-strata be defined taking into account 
people that report more than one race. The Census Bureau, therefore, 
has defined and documented the A.C.E. post-strata to include 
individuals that report more than one race.\102\ The Census Bureau will 
conduct a study of the effects of multiple race reporting after 
completion of the census.
---------------------------------------------------------------------------

    \101\ President, Executive Office, Office of Management and 
Budget, ``Revisions to the Standards for the Classification of 
Federal Data on Race and Ethnicity,'' Federal Register, (30 October 
1997), vol. 62, no. 210, pp. 58782-90.
    \102\ The Census Bureau's plan for including individuals in the 
A.C.E. post-strata who report more than one race is described in 
Griffin and Haines, ``Accuracy and Coverage Evaluation Survey: Final 
Post-stratification Plan for Dual System Estimation,'' 1-2.
---------------------------------------------------------------------------

Making the Final Decision

    The Census Bureau expects that the A.C.E., if properly conducted, 
will make the census more accurate by improving coverage and reducing 
differential undercounts. The Census Bureau will not, however, release 
corrected redistricting data until it has brought its technical 
judgment to bear in assessing the available data to verify that its 
expectations have been met. The Census Bureau will consider operational 
data to validate the successful conduct of the A.C.E., assess whether 
the A.C.E. measurements of undercount are consistent with historical 
patterns of undercount and independent Demographic Analysis benchmarks, 
and review measures of quality.
    In preparing for this determination, the criteria and the process 
that will be followed for the assessment of the A.C.E. results will be 
shared and discussed with outside statistical experts and other 
interested parties in the fall of 2000. This plan is consistent with 
the principle of pre-specification adopted by the Census Bureau for the 
Census 2000 A.C.E. and with its open and transparent planning and 
decision processes. The extent of pre-specification already publicly 
provided is very extensive.
    It should be noted that all major census operations are vulnerable 
to unanticipated difficulties. Such difficulties could affect 
production of the apportionment counts. If, for example, a major 
natural disaster were to occur in a region of the country during census 
nonresponse followup, and this operation were seriously disrupted, the 
Census Bureau might conclude that the apportionment count so 
misrepresented the ``true'' state-by-state population distribution that 
it should not be used until corrective action was taken, possibly 
delaying delivery of the apportionment counts past January 1, 2001. 
Unanticipated difficulties could also affect the A.C.E. The Census 
Bureau would respond to any major unanticipated operational difficulty 
by taking steps to conduct and complete (or repeat, as necessary) all 
planned operations necessary to ensure that an accurate A.C.E. had 
taken place before releasing the statistically corrected data. If the 
Census Bureau determines that incorporating the results of the survey 
would not improve the accuracy of the initial census counts, then the 
uncorrected data would be denominated as the P.L. 94-171 file.
    Secretary Mosbacher's 1991 decision document raised the specter of 
``political tampering'' in any use of statistically corrected census 
data. To avoid even the appearance of political manipulation, the 
Census Bureau has proposed a process for verifying the agency's 
expectations regarding the improvements in accuracy from the A.C.E. 
Under that proposal, a committee

[[Page 38394]]

of senior Census Bureau officials responsible for resolving policy and 
technical issues regarding the A.C.E. and assessing the technical 
effectiveness of its operations would make a recommendation to the 
Census Bureau Director regarding the use of the statistically corrected 
census data. The Director would make a determination regarding the use 
of the statistically corrected data, taking into consideration the 
recommendation of the committee. This committee, known as the Executive 
Steering Committee for A.C.E. Policy (ESCAP), was formed in late 1999 
and normally meets every two weeks to discuss technical and policy 
issues associated with the A.C.E. and to advise the Director on these 
issues. The ESCAP is chaired by the Associate Director for Decennial 
Census and includes the following other senior career staff: Deputy 
Director; Principal Associate Director and Chief Financial Officer; 
Principal Associate Director for Programs; Associate Director for 
Methodology and Standards; Associate Director for Demographic Programs; 
Assistant Director for Decennial Census; Chief, Decennial Statistical 
Studies Division; Chief, Planning, Research and Evaluation Division; 
Chief, Population Division; Chief, Decennial Management Division; and 
Senior Mathematical Statistician. The committee will document its 
discussions and decisions and will make this documentation available 
along with its recommendation to the Director.
    Following the release of census data, the Census Bureau will 
continue its research and evaluation, budget permitting. The census is 
an ongoing process, and the Census Bureau implements refinements to the 
data over a 10-year period. These ongoing efforts are consistent with 
good science and are fundamental to the Census Bureau's work. The fact 
that further research will provide more information about the success 
of census operations, including the production of the apportionment 
counts and the A.C.E., does not alter the requirement to release the 
statistically corrected block-level numbers by the April 1, 2001, 
statutory deadline, if these data meet the Census Bureau's expectations 
with regard to improvements in accuracy. Evaluations of many Census 
2000 operations and results, including the A.C.E., will continue after 
the release of the data; and program evaluation results will be 
available for planning the 2010 census and informing the scientific and 
public discourse over the intervening years.

Conclusions

    The Census Bureau's mission is to produce the most accurate data 
possible, taking into account the intended uses of the data. The 
extensive body of research that the Census Bureau has conducted on 
census undercount, including the 1990 census evaluations, has 
conclusively demonstrated that traditional census methodologies will 
not effectively reduce the differential undercount. The Census Bureau 
has concluded that based on current state-of-the-art science, the best 
method or procedure that has the potential to reduce the differential 
undercount and thereby increase accuracy is the application of 
scientific sampling to improve traditional census methods. This view is 
widespread, though not unanimous, in the professional statistical 
community.
    At the present time, the Census Bureau has also concluded that it 
is operationally feasible to complete the A.C.E. and produce 
statistically corrected census data prior to April 1, 2001, and expects 
that the corrected data will be the most accurate data available. The 
Census Bureau's final decision on what data to release as the most 
accurate data will not be made, however, until the Census Bureau has 
had an opportunity to review the conduct of the census and the A.C.E.

Bibliography

Bell, William R. ``Using Information from Demographic Analysis in 
Post-Enumeration Survey Estimation.'' Journal of the American 
Statistical Association 88 (September 1993): 1106-18.
Belin, T.R., G. J. Diffendal, S. Mack, D.B. Rubin, J.L. Schafer, and 
A.M. Zaslavsky. ``Hierachical Logistic-Regression Models for 
Imputation of Unresolved Enumeration Status in Undercount 
Estimation.'' Journal of the American Statistical Association 88 
(September 1993): 1149-66.
Breiman, Leo. ``The 1991 Census Adjustment: Undercount or Bad 
Data?'' Statistical Science 9, no. 4 (1994): 458-537.
Brown, Lawrence D., Morris L. Eaton, David A. Freedman, Stephen P. 
Klein, Richard A. Olshen, Kenneth W.Wachter, Martin T.Wells, and 
Donald Ylvisaker. ``Statistical Controversies in Census 2000.'' 
Jurimetrics 39 (Summer 1999): 347.
Census Advisory Committee of Professional Associations. 
``Recommendations Made as a Result of the Meeting on April 22-23, 
1999, Recommendation 1.''
Childers, Dan, Gregg Diffendal, Howard Hogan, Nathaniel Schenker, 
and Kirk Wolter. ``The Technical Feasibility of Correcting the 1990 
Census.'' In Proceedings of the Social Statistics Section of the 
American Statistical Association Held in San Francisco, California, 
17-20 August 1987, by the American Statistical Association, 1987.
Childers, Dan and Howard Hogan. ``The 1988 Post Enumeration Survey 
Methods and Preliminary Results.'' In Proceedings of the Survey 
Research Methods Section of the American Statistical Association, 
New Orleans, Louisiana, 22-25 August 1987, by the American 
Statistical Association, 1988.
City of New York v. U.S. Dept. of Commerce. 822 F. Supp. 906, 928 
(E.D.N.Y. 1993).
Cohen, Michael L., Andrew A. White, and Keith F. Rust, eds. 
Measuring a Changing Nation--Modern Methods for the 2000 Census. 
Washington, D.C.: National Academy Press, 1999.
Commerce Secretary's 2000 Census Advisory Committee. ``Final Report, 
Recommendation 3B, Post Enumeration Survey with a Traditional 
Census,'' 22 January 1999.
Department of Commerce v. House of Representatives, 119 S. Ct. 765 
(1999).
Edmonston, Barry, and Charles Schultze, eds. Modernizing the U.S. 
Census Washington, D.C.: National Academy Press, 1995.
Fay, Robert E., Jeffrey S. Passel, J. Gregory Robinson, and Charles 
D. Cowan. The Coverage of Population in the 1980 Census. Washington, 
D.C.: Government Printing Office, 1988.
Fay, Robert E., and John Thompson. ``The 1990 Post Enumeration 
Survey: Statistical Lessons, in Hindsight.'' In Proceedings of the 
1993 Annual Research Conference, 21-24 March 1993, by the Research 
Conference, 1993.
Freedman, David A., and Kenneth W. Wachter, University of 
California. Letter to Rep. Dan Miller, Chairman, House Subcommittee 
on the Census, U.S. House of Representatives. 17 May 2000.
____. ``Planning for the Census in the Year 2000.'' Evaluation 
Review 20 (August 1996): 355-77.
Hogan, Howard. ``The 1990 Post-Enumeration Survey: Operations and 
Results.'' Journal of the American Statistical Association 88 
(September 1993): 1047-67.
____. ``Accuracy and Coverage Evaluation: Theory and Application.'' 
Dual System Estimation Workshop of the National Academy of Sciences 
Panel to Review the 2000 Census. 2 February 2000.
Joint Census Advisory Committees on Race and Ethnic Populations. 
``Recommendations Agreed Upon by the Four Census Advisory Committees 
on the African American, American Indian and Alaska Native, Asian 
and Pacific Islander and Hispanic Populations Made at the Meeting 
Held on May 22-23 1997, Recommendation 3.''
Mulry, Mary, and Bruce D. Spencer. ``Accuracy of the 1990 Census and 
Undercount Adjustments.'' Journal of the American Statistical 
Association 88 (September 1993): 1080-91.
Norwood, Janet L., Chair, National Academy of Sciences Panel to 
Review the 2000 Census. Letter to Kenneth Prewitt, U.S. Department 
of Commerce, Bureau of the Census, 3 May 1999.

[[Page 38395]]

Robinson, J.G., B. Ahmed, P. Das Gupta, and K. A. Woodrow. 
``Estimates of Population Coverage in the 1990 United States Census 
Based on Demographic Analysis.''
Journal of the American Statistical Association 88 (September 1993): 
1061-77.
Steffey, Duane L., and Norman M. Bradburn. Counting People in the 
Information Age. Washington, D.C.: National Academy Press, 1994.
U.S. Bureau of the Census. ``Accuracy and Coverage Evaluation: The 
Design Document.'' By Danny R. Childers. DSSD Census 2000 Procedures 
and Operations Memorandum Series Chapter S-DT-01.
____. ``Accuracy and Coverage Evaluation: Overview of Design.'' By 
Danny R. Childers and Deborah A. Fenstermaker, 11 January 2000.
____. ``Accuracy and Coverage Evaluation Survey: Dual System 
Estimation.'' By Donna Kostanich and Richard Griffin, 12 January 
2000.
____. ``Accuracy and Coverage Evaluation Survey: Final Post-
stratification Plan for Dual System Estimation.'' By Richard Griffin 
and Dawn Haines. DSSD Census 2000 Procedures and Operations 
Memorandum Series Chapter Q-24, 19 April 2000.
____. ``Accuracy and Coverage Evaluation Survey: Targeted Extended 
Search Plans.'' By Alfredo Navarro. DSSD Census 2000 Procedures and 
Operations Memorandum Series Chapter Q-18, 12 January 2000.
____. ``Additional Research on Accuracy of Adjusted Versus 
Unadjusted 1990 Census Base for Use in Intercensal Estimates.'' 
Addendum to Report of the Committee on Adjustment of Post Censal 
Estimates, 25 November 1992.
____. ``Analysis of CAPE Findings on 1990 PES Technical Issues.'' By 
Sally M. Obenski, 9 June 2000.
____. ``Analysis of CAPE Findings on PES Accuracy at Various 
Geographic Levels.'' By Sally M. Obenski and Robert E. Fay, 9 June 
2000.
____. ``An Analysis of the Consistency of the 1990 Mosbacher 
Guidelines to U.S. Census Bureau Standards.'' By Sally M. Obenski 
and Robert E. Fay, 16 May 2000.
____. ``Assessment of Accuracy of Adjusted Versus Unadjusted 1990 
Census Base for Use in Intercensal Estimates,'' Report of the 
Committee on Adjustment of Postcensal Estimates, 7 August 1992.
____. ``Characteristics of Census Errors.'' By Deborah Griffin and 
Christopher Moriarity. 1990 Decennial Census Preliminary Research 
and Evaluation Memorandum No. 179, 15 September 1992.
____. ``Master Activity Schedule for Census 2000.''
____. ``Minutes of the Executive Steering Committee on Accuracy and 
Coverage Evaluation (A.C.E.) Policy (ESCAP),'' 5 January 2000.
____. ``Non-Response in Census Coverage Measurement Surveys and Its 
Impact ``An Historical Review.'' By Ruth Ann Killion. DSSD Briefs, 
Information, and Topics Memorandum Series No. 44C, 17 September 
1998.
____. ``Reinventing the Decennial Census.'' Global Report of the 
Task Force for Planning the Year 2000 Census, June 1995.
____. ``Report of the Working Group on the Use of Demographic 
Analysis in Census 2000.'' By William R. Bell, Campbell J. Gibson, 
Prithwis Das Gupta, Gregory K. Spencer, J. Gregory Robinson, Mary H. 
Mulry, Elizabeth A. Vacca, Robert E. Fay, and Charlene A. Leggieri, 
6 May 1996.
____. ``Report to Congress--The Plan for Census 2000.'' Originally 
issued July 1997, revised and reissued August 1997.
____. ``Some Results from the Census 2000 Dress Rehearsal.'' By 
Rajendra Singh. DSSD Census 2000 Dress Rehearsal Memorandum Series 
A-76, 26 February 1999
____. ``Technical Assessment of the Accuracy of Unadjusted Versus 
Adjusted 1990 Census Counts.'' Report of the Undercount Steering 
Committee, 21 June 1991.
____. ``Updated Summary: Census 2000 Operational Plan,'' February 
1999.
U.S. Bureau of Labor Statistics. Abraham, Katharine, Letter to Harry 
A. Scarr, U.S. Department of Commerce, Bureau of the Census, 1 
December 1993.
U.S. Congress. House. Decennial Census Improvement Act of 1991, 
102nd Cong., 2nd sess., H.R. 3280. Congressional Record. Daily ed. 
(9 October 1991), H7694.
____. Committee on Government Reform and Oversight. Prepared 
Testimony of K.W. Wachter and D.A. Freeman Before the House 
Committee on Government Reform and Oversight, 104th Cong., 1st 
sess., 29 February 1996.
U.S. Department of Commerce. ``Adjustment of the 1990 Census for 
Overcounts and Undercounts of Population and Housing: Notice of 
Final Decision.'' Federal Register (22 July 1991) vol. 56 pp. 33582-
642.
____. ``Census 2000 Dress Rehearsal Shows Undercount Persist; 
Scientific Methods Correct Race and Ethnic Differential.'' Commerce 
News, 20 April 1999, CB 99-CN. 16 (revised).
____. ``Decision of the Director of the Bureau of the Census on 
Whether to Use Information from the 1990 Post Enumeration Survey 
(PES) to Adjust the Base for the Intercensal Population Estimates 
Produced by the Bureau of the Census.'' Federal Register (4 January 
1993) vol. 58, no. 1, pp. 69-78.
____. ``Final Guidelines for Considering Whether or not Statistical 
Adjustments of the 1990 Decennial Census of Population and Housing 
Should be Made for Coverage Deficiencies of the Population.'' 
Federal Register (15 March 1990) vol. 55, p. 9838.
____. ``Position on Adjustment of the 1980 Census Counts for 
Underenumeration.'' Federal Register (16 December 1980) vol. 45, no. 
243, pp. 82872-85.
U.S. General Accounting Office. Decennial Census: 1990 Results Show 
Need for Fundamental Reform. Report to Congressional Requesters, 9 
June 1992, 49 GAO/GGD-92-94.
U.S. President, Executive Office. Office of Management and Budget. 
``Revisions to the Standards for the Classification of Federal Data 
on Race and Ethnicity.'' Federal Register (30 October 1997) vol. 62, 
no. 210, pp. 58782-90.
Wachter, Kenneth, and David Freedman. ``Local Heterogeneity and 
Census Adjustment for the Intercensal Base.'' Technical Report No. 
381. Berkeley, CA: University of California, Department of 
Statistics, 1993.
White, Andrew A., and Keith F. Rust, eds. Sampling in the 2000 
Census: Interim Report I. Washington, D.C.: National Academy Press, 
1996.
____. Preparing for the 2000 Census: Interim Report II. Washington, 
D.C.: National Academy Press, 1997.
Wolter, Kirk M. ``Some Coverage Error Models for Census Data.'' 
Journal of the American Statistical Association 81 (June 1986): 338-
46.
Wright, Tommy and Joyce Farmer. ``A Bibliography of Selected 
Statistical Methods and Development Related to Census 2000.'' 3rd 
ed., 1 May 2000.

June 13, 2000.

MEMORANDUM FOR KENNETH PREWITT

From: William M. Daley
    Attached is my decision adopting the analysis and conclusions 
set forth in ``Accuracy and Coverage Evaluation: Statement on the 
Feasibility of Using Statistical Methods to Improve the Accuracy of 
Census 2000.''
    The Department of Commerce and the Census Bureau are committed 
to making certain that the decennial census, the largest peacetime 
mobilization in our country's history, produces the most accurate 
count possible of the individuals in our Nation. The census is an 
important civic undertaking designed to find out who we are and how 
we live. We owe it to the American people to use all of the tools at 
our disposal to make the census as accurate as possible.
    For decades, the experts at the Census Bureau and within the 
statistical community have recognized that the methodology used in 
the past fails to count many Americans. This phenomenon `` called 
the undercount `` has been measured since the 1940s. More 
disturbing, however, is the established fact that the undercount 
operates differently for different population groups, creating an 
inequity called the differential undercount. Despite the Census 
Bureau's best efforts, the differential undercount has persisted 
and, for at least the last 50 years, has meant that some groups in 
the population are undercounted and therefore underrepresented in 
political, resource-allocation, and other decisions.
    The choice we face is whether to use modern statistical methods 
to produce a more accurate census, or whether we do nothing. Under 
the law, statistical methods may not be used in tabulating the 
population for purposes of apportioning seats in the House of 
Representatives, but I am required to authorize the use of modern 
statistical methods, if ``feasible,'' for all other releases of 
census data.

[[Page 38396]]

    The Director of the Census, with guidance from the Department 
concerning the relevant legal standard, has provided an analysis of 
the feasibility of using statistical sampling to correct the 
persistent errors in the census and to improve its accuracy--
``Accuracy and Coverage Evaluation: Statement on the Feasibility of 
Using Statistical Methods to Improve the Accuracy of Census 2000.'' 
As explained in that document, absent the use of statistical methods 
there is no way to correct the persistent differential undercount in 
Census 2000. With established statistical methods, however, the 
Census Bureau believes that it will be able to correct these errors 
and improve the overall accuracy of the census by increasing 
coverage and reducing the differential undercount.
    I hereby adopt the analysis and conclusions of the Director of 
the Census set forth in ``Accuracy and Coverage Evaluation: 
Statement on the Feasibility of Using Statistical Methods to Improve 
the Accuracy of Census 2000.'' As explained in that document, the 
expert staff at the Bureau believe that the Accuracy and Coverage 
Evaluation Survey, which was designed to measure and correct for the 
overall undercount and the differential undercount, should make the 
census counts more accurate. As is appropriate, however, no final 
decision about whether to correct the census counts can be made 
until the operations have been completed and considered by the 
Bureau. The Director will make a final decision before April 1, 
2001, the deadline by which the Bureau must provide data to the 
States for redistricting.
    I am also proposing today a regulation that will insulate the 
final decision on whether to correct the census counts from even the 
appearance of political tampering and will make the decision-making 
process as transparent as possible. Because the final decision on 
whether to correct the census is a technical decision, the proposed 
regulation would delegate my authority over that decision to the 
Director of the Census. His decision would, in turn, be informed by 
a public recommendation made by a group of career experts at the 
Census Bureau. Through this process, we will be able to ensure 
public confidence in the final decision.

    Dated: June 13, 2000.
William M. Daley,
Secretary of Commerce.


June 12, 2000.
MEMORANDUM TO: The Secretary, The Director of the Census
FROM: Andrew J. Pincus
SUBJECT: Legal Obligation to Produce Statistically-Corrected Non-
Apportionment Census Numbers

    As you know, the Department of Commerce and the Census Bureau 
have been reviewing what process to use in determining whether to 
statistically correct census data for purposes other than 
apportionment of the House of Representatives. As part of this 
review, we have examined the legal requirements of the Census Act. 
After careful analysis, we have concluded that Section 195 of the 
Census Act requires the Census Bureau, if feasible, to produce 
statistically-corrected numbers from the decennial census for all 
non-apportionment purposes.
    The feasibility determination is a technical decision that 
should be made by the Director, to whom the Secretary delegated his 
Title 13 responsibilities in Departmental Organizational Order 35-2A 
(July 22, 1987). To this end, we also believe it appropriate to 
propose a regulation that would make certain that the Director has 
final authority over the feasibility determination.

I. Background

    The Constitution requires Congress to apportion seats in the 
House of Representatives among the States every ten years based on 
the results of the decennial census, providing that ``[t]he actual 
Enumeration shall be made within three Years after the first Meeting 
of the Congress of the United States, and within every subsequent 
Term of ten Years, in such Manner as they [Congress] shall by Law 
direct.'' \1\ Through the Census Act, which is codified in title 13 
of the United States Code, Congress has delegated its broad 
authority over the census to the Secretary of Commerce.\2\ In 
particular, 13 U.S.C. 141(a) provides that the Secretary of Commerce 
shall take ``a decennial census of [the] population * * * in such 
form and content as he may determine, including the use of sampling 
procedures and special surveys.'' As the Supreme Court recognized in 
Wisconsin v. City of New York, the Secretary's determination as to 
how to conduct the Census, pursuant to the delegation of authority 
provided to him by Congress, need only be reasonable, so long as it 
is also ``consistent with the constitutional language and the 
constitutional goal of equal representation.'' Id. at 19. The Court 
further recognized, in the context of the Secretary's decision in 
1990 not to adjust the census, that the ``Constitution itself 
provides no real instruction'' on what methods the Secretary should 
use in performing the Census. Id. at 18.
---------------------------------------------------------------------------

    \1\ Constitution, Art. I, Sec. 2, Cl. 3.
    \2\ Wisconsin v. City of New York, 517 U.S. 1 (1996).
---------------------------------------------------------------------------

II. Section 195 of the Census Act Requires the Census Bureau To Use 
Sampling When ``Feasible'' For Calculating the Population For Purposes 
Other Than Apportionment of Seats in the House of Representatives Among 
the States

    Section 195 of the Census Act states:

    Except for the determination of population for purposes of 
apportionment of Representatives in Congress among the several 
States, the Secretary shall, if he considers it feasible, authorize 
the use of the statistical method known as ``sampling'' in carrying 
out the provisions of this title.

13 U.S.C. 195. Section 195 refers specifically to only one of the many 
uses of census data. Decennial census data are used not only by the 
U.S. Congress for apportioning seats in the House of Representatives 
among the States, but also by the States in drawing the lines for 
congressional and state and local legislative districts, and by federal 
and state agencies in allocating funds.
    In Department of Commerce v. House of Representatives, 119 S. Ct. 
765 (1999), the Supreme Court held that Section 195 does not permit the 
use of sampling to produce population counts for the purpose of 
apportioning seats in the House of Representatives among the States. 
Id. at 777 (``there is only one plausible reading of the amended 
Sec. 195: It prohibits the use of sampling in calculating the 
population for purposes of apportionment.''). Here, the question is 
what standard Section 195 applies with respect to the calculation of 
population by the Census Bureau for purposes other than ``apportionment 
of Representatives in Congress among the several States.'' The plain 
language of the provision supplies the answer: Section 195 states that 
the Secretary ``shall'' authorize the use of statistical sampling for 
all other purposes ``if he considers it feasible.'' Thus, when 
calculating population or other information for a purpose other than 
apportionment, the Secretary (or his designee, the Census Bureau) must 
first determine whether it is ``feasible'' to use sampling, and--if the 
use of sampling is feasible--its use must be authorized.
    This interpretation of Section 195's plain language is confirmed by 
Congress's amendment of the provision in 1976. Prior to that amendment, 
Section 195 stated:

    Except for the determination of population for apportionment 
purposes, the Secretary may, where he deems it appropriate, 
authorize the use of the statistical method known as `sampling' in 
carrying out the provisions of this title.

The pre-1976 wording (``may, where he deems it appropriate'') gave the 
Secretary the option of using sampling. The 1976 amendment eliminated 
the Secretary's discretion, transforming Section 195 into a mandatory 
directive --the Secretary ``shall * * * authorize the use of'' sampling 
for all other purposes ``if he considers it feasible.'' The Census Act 
therefore unambiguously requires, with respect to non-apportionment 
calculations, that when sampling is feasible, it must be used.
    The Supreme Court's recent decision in Department of Commerce v. 
House of Representatives confirms this conclusion. In explaining the 
purpose of the 1976 amendments, the Court stated, ``[t]hey changed a 
provision that permitted the use of sampling for purposes other than 
apportionment into one that required that sampling be used for such 
purposes if `feasible.' 119 S.Ct. at 778. The Court explained that

[[Page 38397]]

``section [195] now requires the Secretary to use statistical sampling 
in assembling the myriad demographic data that are collected in 
connection with the decennial census. But the section maintains its 
prohibition on the use of statistical sampling in calculating 
population for purposes of apportionment.'' 119 S.Ct. at 777.

III. The Census Bureau's Calculation of Population for the Purpose of 
Redistricting is Subject to Section 195's ``Feasib[ility]'' Standard

    Section 141(c) of the Census Act permits the ``officers or public 
bodies having initial responsibility for the legislative apportionment 
or districting of each State'' to submit to the Secretary ``a plan 
identifying the geographic areas for which specific tabulations of 
population are desired.'' The same provision directs the Secretary to 
report such ``[t]abulations of population,'' as well as the ``basic 
tabulations of population'' for States that have not submitted a plan, 
within one year of the decennial census date. It is clear that these 
population tabulations are not ``the determination of population for 
purposes of apportionment of Representatives in Congress among the 
several States'' (Section 195), and therefore are subject to Section 
195's directive that the use of sampling ``shall'' be authorized if 
``feasible.''
    To begin with, the population tabulations supplied to the States 
pursuant to Section 141(c) simply are not made or used for purposes of 
apportioning seats in the House of Representatives among the States. 
Section 141(c) makes clear that it relates to tabulations for 
``legislative apportionment or districting of each State.'' And a 
separate subsection of Section 141--subsection (b)--governs the 
``tabulation of total population by States * * * as required for the 
apportionment of Representatives in Congress among the several 
States.'' Indeed, the distinction between these two groups of 
calculations is confirmed by their different due dates: the latter set 
of numbers must be completed three months earlier than the 
redistricting information required by Section 141(c). See also Section 
141(e)(2) (distinguishing between use of census data for 
``apportionment of Representatives in Congress among the several 
States'' and for ``prescribing congressional districts'').
    Some commentators have suggested that the term ``apportionment'' 
within Section 195's ``[e]xcept'' clause encompasses population 
calculation for the purposes of redistricting as well as for the 
purpose of allocating seats in the House of Representatives among the 
States. That position is inconsistent with the plain language of the 
statute. First, it ignores the clear distinction in Section 141 between 
these two categories of calculations. Second, Congress in 1976 revised 
the ``[e]xcept'' clause, replacing the word ``apportionment'' with the 
phrase ``apportionment of Representatives in Congress among the Several 
States.'' It is difficult to imagine how Congress could have more 
clearly evidenced its intent to limit Section 195's prohibition against 
the use of sampling to the calculation of population used to allocate 
among the States seats in the House of Representatives. And because 
Section 141(c) specifically refers to tabulations for redistricting 
purposes, but that reference does not appear in the ``[e]xcept'' clause 
of Section 195, it is plain that redistricting tabulations are not 
encompassed within the Section 195 prohibition. \3\
---------------------------------------------------------------------------

    \3\ Some commentators have argued that the Supreme Court reached 
a different conclusion in Department of Commerce because it found 
standing ``on the basis of the expected effects of the use of 
sampling in the 2000 census on intrastate redistricting'' (119 S. 
Ct. at 774). The Court's standing decision, however, simply reflects 
a conclusion that an individual claiming injury by the use of that 
data for redistricting had alleged sufficient Article III injury in 
fact to challenge the plan. But the Census plan before the Court 
provided for the collection and production of a single set of 
sampling-adjusted data for use in both the apportionment tabulation 
and the redistricting tabulation. Because the Court invalidated the 
plan, there was no need for the Court to apply Section 195 to the 
use of sampling for redistricting purposes in order to redress these 
plaintiffs' purported injury. This conclusion is confirmed by the 
Court's careful limitation of its holding: ``The District Court 
below * * *  concluded that the proposed use of statistical sampling 
to determine population for purposes of apportioning congressional 
seats among the States violates the Act. We agree.'' 119 S. Ct. at 
765.
---------------------------------------------------------------------------

    Finally, some commentators have suggested that as a practical 
matter these two sets of numbers are inextricably linked, asserting--
for example--that it would be a plainly improper result if the Section 
141(c) population tabulation of a State for redistricting purposes did 
not equal the Section 141(b) apportionment population tabulation for 
that State. Nothing in the Census Act requires that result and, 
moreover, the two totals have not been equal in the past. For example, 
government personnel stationed overseas are included in a State's 
Section 141(b) tabulation, but are not included in the data provided to 
that State under Section 141(c). Congress could have required such 
equality in either Section 141 or Section 195, but it did not do so. 
Rather, Congress in Section 141 expressly distinguished between the two 
categories of calculations.
    The Census Act thus clearly directs that statistical sampling 
``shall'' be used in tabulating population for the purposes set forth 
in Section 141(c) if the Secretary considers it ``feasible'' to do so. 
Even if the plain language of the Act were not clear on this point, we 
believe that this interpretation is most consistent with the purposes 
of the Census Act and that adopting such an interpretation is within 
your discretion. In Wisconsin v. City of New York, 517 U.S. 1 (1996), 
the Supreme Court unanimously concluded ``the wide discretion bestowed 
by the Constitution upon Congress, and by Congress upon the 
Secretary,'' mandates substantial judicial deference to the Secretary's 
determinations with respect to the decennial census (517 U.S. at 19). 
Given the long history of the use of sampling by the Census Bureau, and 
the importance of obtaining the most accurate population tabulations 
possible--because of the constitutional significance of the ``one 
person, one vote'' principle and of the equal protection principles 
reflected in the Voting Rights Act--interpreting the statute to permit 
the use of sampling when feasible is the most appropriate approach. The 
alternative interpretation would bar the use of statistical sampling 
even if the use of sampling would lead to more accurate results, a 
construction that conflicts with the basic goal of the decennial 
census--to obtain an accurate count of the persons within the United 
States.

IV. The Standard For the Feasibility Determination

    Section 195 does not contain a definition of the term ``feasible.'' 
The dictionary definition of the term ranges from the most common 
``capable of being done or carried out'' to ``capable of being used or 
dealt with successfully, suitable'' or ``reasonable, likely.'' 
Webster's Ninth New Collegiate Dictionary (1990). The Supreme Court has 
considered the word ``feasible'' in other contexts and found that the 
plain meaning of the term generally denotes the first and broadest 
definition--``capable of being done.'' In American Textile Mfrs. 
Institute, Inc. v. Donovan, 452 U.S. 490, 509 (1981), the Court 
interpreted the term ``to the extent feasible'' to preclude the 
Secretary of Labor from engaging in a cost-benefit analysis of a public 
health standard; as the Court explained, Congress itself, by requiring 
a standard ``to the extent feasible'' had made the policy choice for 
the Secretary. See also Citizens to Preserve Overton Park, Inc. v. 
Volpe, 401 U.S. 402, 411 (1971) (``the requirement that there be no 
'feasible

[[Page 38398]]

alternative' route admits of little administrative discretion.'').
    We understand the term ``feasible'' in accordance with its ordinary 
meaning and the overall purposes of the Census Act. It also must be 
understood in terms of the uses to which non-apportionment census data 
are put, including, among other things, redistricting and allocation of 
federal funds. While in other contexts it might be appropriate to 
understand ``feasible'' to mean ``possible,'' given the obvious 
importance of obtaining the most accurate population (and other) 
tabulations possible, it would seem most appropriate to construe that 
term in a manner that focuses upon promoting accurate census results. 
\4\ Thus, with respect to the proposed use of statistical sampling for 
data to be released to the States under Section 141(c), such use is 
``feasible'' within the meaning of Section 195 if (1) the proposed use 
of sampling is compatible with the other aspects of the census plan, 
and with any statutory, timing, and funding constraints; and (2) the 
proposed use of statistical sampling would improve the overall accuracy 
of the census data.
---------------------------------------------------------------------------

    \4\ Of course, in other contexts where there is no independent 
requirement that the population court be conducted without the use 
of sampling (unlike the decennial census, where the statue as 
construed by the Supreme Court prohibits the use of sampling for 
apportionment of seat in the House of Representatives), the analysis 
might also take greater account of the efficiencies that could be 
gained by substituting sampling for those other methods.
---------------------------------------------------------------------------

    The two components of ``feasibility `` can be termed ``operational 
feasibility'' and ``technical feasibility.'' These are matters that are 
properly within the expert judgment of the Census Bureau. The Census 
Bureau's extensive experience in the conduct of the census, the use of 
statistical sampling techniques, and the measurement of accuracy should 
be the basis for these essentially technical judgments.

V. The Decisionmaking Process

    The determination whether the use of sampling is ``feasible'' under 
Section 195 should be based upon the information before the 
decisionmaker at the time the determination is made. Public Law No. 94-
171 requires the Census Bureau to deliver official census data to the 
states for redistricting purposes by April 1, 2001. 13 U.S.C. 141(c). 
As with every decennial census, the Census Bureau will conduct 
extensive analyses on the census data in the ensuing years. In order to 
make a final decision on whether to deliver statistically corrected 
data for redistricting purposes, the Census Bureau need only consider 
the evidence available to it at the time of its decision to determine 
whether the statistically corrected numbers are more accurate and 
therefore that the use of sampling is ``feasible'' as that term is 
defined herein. See, e.g., Vermont Yankee Nuclear Power Corp. v Natural 
Resources Defense Council, 435 U.S. 519, 552-54 (1978) (review of 
agency decision must be made based on information available at the time 
the decision was made); ICC v. New Jersey, 322 U.S. 503, 514 (1970).
    The Census Bureau is in the process of completing a document which 
will provide information concerning its assessment of whether using 
statistically sampling is feasible with respect to the release of P.L. 
94-171 data. Although, as the document will indicate, the Census Bureau 
has determined that the use of statistical sampling is operationally 
feasible and should improve the accuracy of the census, no final 
decision will be made with respect to the release of data until after 
the Bureau has had the opportunity to review whether census operations 
were conducted in a way that met expectations. This document will be 
published in the Federal Register, along with a proposed regulation 
that would delegate to the Director of the Census the Secretary of 
Commerce's authority to make the final, technical decision on what 
numbers to release and would set forth a process for the Census 
Bureau's consideration of what numbers to release.

Robert J. Shapiro,
Under Secretary for Economic Affairs.
[FR Doc. 00-15348 Filed 6-14-00; 8:45 am]
BILLING CODE 3510-07-P