Estimation of Population Coverage in the 1990 United States Census Based on Demographic Analysis

Article excerpt

1. INTRODUCTION

The general method of demographic analysis as a tool for coverage evaluation is well developed and has been actively used at the Census Bureau to assess the completeness of coverage in every census since 1960. (See Siegel and Zelnik 1966; U.S. Bureau of the Census 1974; and U.S. Bureau of the Census 1988 for the basic demographic evaluations of the 1960, 1970, and 1980 censuses.) Demographic analysis estimates of coverage have become the benchmark by which national differences in coverage for age, sex, and race groups and changes in coverage over time are measured.

The purpose of the demographic analysis evaluation program for 1990 has been twofold: (1) to evaluate the completeness of coverage of population in the 1990 census based on demographic analysis, and (2) to develop a statistically based assessment of the accuracy of those demographic estimates of net coverage. This article reports the results of the demographic estimates of coverage for 1990 and the assessment of the accuracy of the estimates. An important byproduct of the demographic program is the historical estimates of coverage provided for every census since 1940. The demographic estimates of net coverage for 1990 were also used to evaluate the overall quality of the national estimates of net coverage based on the 1990 Post-Enumeration Survey (PES). (See Hogan 1992 for a description of the PES.)

Section 2 describes the methodology of the demographic estimates. Section 3 describes the estimates of coverage in the 1990 census based on demographic analysis and compares the estimates with those for previous censuses. Section 4 presents the results of the first-time assessment of uncertainty in the demographic coverage estimates for 1990. Section 5 presents our conclusions and plans for future research.

2. THE GENERAL METHOD OF DEMOGRAPHIC ANALYSIS

Estimation of census coverage based on demographic analysis involves developing demographic estimates of the resident population in various categories, such as age-sex-race groups, by combining various sources of administrative and demographic data. The independent population estimates (P) are then compared with the corresponding census counts (C) to yield an estimate of the net census undercount, u, and net undercount rate, r:

u = P - C (1)

and

r = (u/P)*100. (2)

Demographic analysis represents a macro-level approach to measuring coverage, where analytic estimates of net undercount are derived by comparing aggregate sets of data or counts. This approach differs fundamentally from the PES, which represents a micro-level approach where estimates of coverage are based on case-by-case matching with census records for a sample of the population.

The particular analytic procedure used to estimate coverage nationally in 1990 for the various demographic subgroups depends primarily on the nature and availability of the required demographic data. Different demographic techniques were used for the populations under age 55, 55-64, and 65 and over; the total population is the sum of these subgroups. Figure 1 summaries the cohort estimation procedure for each group.

2.1 Estimation of Subgroups

2.1.1 Age under 55. The demographic analysis estimates for the population below age 55 in 1990 are based on the compilation of historical estimates of the components of population change: births (B), deaths (D), immigration (I), and emigration (E). Presuming that the components are accurately measured, the population estimates ([P.sub.1]) are derived by the basic demographic accounting equation applied to each cohort:

[P.sub.1] = B - D + I - E. (3)

For example, the estimate of the population age 40 on April 1, 1990 is based on births from April 1949 to March 1950 (adjusted for underregistration), reduced by deaths to the cohort in each year between 1950 and 1990, and incremented by estimated immigration and emigration of the cohort over the 40-year period. …