APPENDIX D
Population Estimates

The Census Bureau has long had an active program of using demographic analysis to develop updated estimates of total population and population by age for various levels of geography, such as states, counties, and cities. The Census Bureau's state-and county-level models of school-age children who were poor in 1993 use county and state postcensal population estimates for age groups as of July 1994; these estimates were developed within the framework of the Census Bureau's population estimates program (Long, 1993).

TOTAL POPULATION ESTIMATES

Total population estimates are developed by the component method of demographic analysis. In general, the component method starts from an area's population in the previous census. That number is then updated by the net demographic change—adding births and international immigration and subtracting deaths and emigration. The final component, internal migration or migration to and from other parts of the United States, is currently estimated from administrative records. No adjustments are made for the estimated net population undercount in the census.

Postcensal county estimates of total population are produced by the component method, with three elements: (1) the numbers of births and deaths are based on reported vital statistics for each county; (2) reports of the Immigration and Naturalization Service are used to estimate net immigration from abroad; and (3) administrative records are used to estimate net migration between counties. Net migration of people under 65 years of age is estimated for each county from a year-to-year match of federal income tax returns; for people aged 65 and over, net



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 69
Small-Area Estimates of School-Age Children in Poverty: Interim Report I: Evaluation of 1993 County Estimates for Title I Allocations APPENDIX D Population Estimates The Census Bureau has long had an active program of using demographic analysis to develop updated estimates of total population and population by age for various levels of geography, such as states, counties, and cities. The Census Bureau's state-and county-level models of school-age children who were poor in 1993 use county and state postcensal population estimates for age groups as of July 1994; these estimates were developed within the framework of the Census Bureau's population estimates program (Long, 1993). TOTAL POPULATION ESTIMATES Total population estimates are developed by the component method of demographic analysis. In general, the component method starts from an area's population in the previous census. That number is then updated by the net demographic change—adding births and international immigration and subtracting deaths and emigration. The final component, internal migration or migration to and from other parts of the United States, is currently estimated from administrative records. No adjustments are made for the estimated net population undercount in the census. Postcensal county estimates of total population are produced by the component method, with three elements: (1) the numbers of births and deaths are based on reported vital statistics for each county; (2) reports of the Immigration and Naturalization Service are used to estimate net immigration from abroad; and (3) administrative records are used to estimate net migration between counties. Net migration of people under 65 years of age is estimated for each county from a year-to-year match of federal income tax returns; for people aged 65 and over, net

OCR for page 69
Small-Area Estimates of School-Age Children in Poverty: Interim Report I: Evaluation of 1993 County Estimates for Title I Allocations migration is estimated for each county from the change in Medicare enrollment figures (Bureau of the Census, 1995b). The county population totals are summed for each state to provide estimates of the total population of each state. All county and state population totals are then adjusted to sum to independently derived estimates of the total U.S. population. The county estimates are also reviewed locally under the Census Bureau's Federal State Cooperative Program for Local Population Estimates. ESTIMATES BY AGE Estimates by age group are prepared separately, but within the framework of the total population estimates for states and counties. Specifically, county age estimates are prepared in a two-step procedure. In the first step, estimates of total county population are developed as described above. In addition, estimates of state population by single years of age, sex, race, and Hispanic origin are developed. The state age estimates (which are controlled to the state total population estimates) use a component method in which migration rates by age are derived from school enrollment data (Bureau of the Census, 1987). In the second step, the county age estimates are developed by using a raking ratio adjustment of the estimates from the previous census. In this approach, the beginning matrix of counts for each county by age, sex, race, and Hispanic origin from the previous census is simultaneously adjusted to agree with the postcensal estimate of the total county population and the postcensal estimates for the applicable state by age, sex, race, and Hispanic origin (Sink, 1996). This procedure means that the errors in the county estimates of an age group reflect errors in the assumption that the age distribution of each county within a state changes in the same manner as that state's age distribution. The errors in the county estimates of an age group also reflect errors in the derivation of the state estimates of age groups and errors in the derivation of the county estimates of total population. As more data that reflect population change have become available and accessible, the methods for developing updated population estimates for geographic areas have changed, and the estimates have improved. The Census Bureau evaluates its estimates at regular 10-year intervals by comparisons with the decennial census figures. Also, the continuing research and evaluation program helps to determine the best approaches for improved performance (Davis, 1994). ESTIMATES OF RELATED CHILDREN For estimating numbers of poor school-age children, the Census Bureau's state-and county-level regression models use population estimates for the noninstitutionalized population under age 21 (county-level model) and the noninstitutionalized population under age 65 and the noninstitutionalized population

OCR for page 69
Small-Area Estimates of School-Age Children in Poverty: Interim Report I: Evaluation of 1993 County Estimates for Title I Allocations aged 5–17 (state-level model). These estimates are developed by subtracting administrative records counts of institutionalized people in the relevant age groups from the demographic estimates developed as described above. Finally, the Census Bureau provides to the Department of Education estimates of related children aged 5–17 for counties as of July 1994 to use as denominators in calculating county poverty rates to use in the Title I allocations. (The numerators are the Census Bureau's estimates of the number of related school-age children in each county who were poor in 1993, developed as described in Appendix C.) These estimates of related children are developed by adjusting the population estimates of noninstitutionalized children aged 5–17 on the basis of the ratio of related children aged 5–17 to noninstitutionalized children aged 5–17 for each county in the 1990 census.