Criteria for selecting a suitable method for producing post-2000 county population estimates: A case study of population estimates in Illinois

We compared 2000 county population estimates for Illinois against 2000 census counts. Administrative records (ADREC) and ratio correlation (Ratio-CORR) methods were used to produce two sets of controlled county estimates for 2000; a third set represented an average of the estimates reached using these methods. Another set using the ADREC method was not controlled to any estimate. Also, the 2000 estimates were adjusted for undercount in the 1990 census. We compared performance of these methods with the performance of two naive models: (i) do nothing and (ii) constant growth rate. ADREC estimates were more accurate than estimates from the Ratio-CORR or Average method in terms of Mean Absolute Percent (MAPE) or weighted MAPE. Undercount adjustment in general improved the accuracy of the estimates for all three methods. A top-down or bottom-up approach worked equally well. As a single method, ADREC performed best.     

MAPE-R: a rescaled measure of accuracy for cross-sectional subnational population forecasts

Accurately measuring a population and its attributes at past, present, and future points in time has been of great interest to demographers. Within discussions of forecast accuracy, demographers have often been criticized for their inaccurate prognostications of the future. Discussions of methods and data are usually at the centre of these criticisms, along with suggestions for providing an idea of forecast uncertainty. The measures used to evaluate the accuracy of forecasts also have received attention and while accuracy is not the only criterion advocated for evaluating demographic forecasts, it is generally acknowledged to be the most important. In this paper, we continue the discussion of measures of forecast accuracy by concentrating on a rescaled version of a measure that is arguably the one used most often in evaluating cross-sectional, subnational forecasts, Mean Absolute Percent Error (MAPE). The rescaled version, MAPE-R, has not had the benefit of a major empirical test, which is the central focus of this paper. We do this by comparing 10-year population forecasts for U.S. counties to 2000 census counts. We find that the MAPE-R offers a significantly more meaningful representation of average error than MAPE in the presence of substantial outlying errors, and we provide guidelines for its implementation.     

Estimating historic population data for small geographies using census housing information

Historical population data for small geographies (e.g. blocks, block-groups, and census tracts) are not available for periods earlier than 1980. In this research note, we propose a geographically-constrained housing unit method (GHUM) to estimate historic population for small geographies using housing age data available in the 1980–2000 censuses. The GHUM is a two-stage method. The first stage follows a traditional housing unit method and provides initial household and group quarter population estimates for small geographies. The second stage takes advantage of the availability of historic data for larger geographies (e.g. counties, states) to adjust the first stage estimates and to provide final estimates. The GHUM is used to estimate 1940–1990 county population and census tract population in Kentucky. The quality of the population estimates is assessed. A two-sample Kolmogorov–Smirnov test indicates that these estimates are statistically reliable at the 10 % significance level.     

New african American life tables from 1935–1940 to 1985–1990*

New life tables for African Americans are presented from 1935 through 1990. They are based on a historical series of vital statistics data on deaths that have been corrected for age misreporting, on reconstructed population counts that have been adjusted for census underenumeration, and on births that have been corrected for underregistration. The new life tables show rapid mortality declines for both African American males and females from 1935 to 1950, and relatively steady reductions thereafter for females. The smaller declines in male mortality in young adulthood and middle age since the 1950s have led to exceptionally high ratios of male to female mortality at these ages. Corrections for census undercounts lead to higher values of life expectancy than in official life tables, but to less improvement over time. Official estimates of life expectancy at age 65 appear to be about 10% too high around 1940 but only about 1.5% too high in the late 1980s.     

Estimates of coverage of the population by sex,race, and age in the 1970 census

Several estimates of total net underenumeration and of net census errors by sex, race (white, Negro-and-other-races, Negro), and age (five-year groups) in the 1960 and 1970 Censuses, for the total population of the United States, derived by the methods of demographic analysis, are presented. The different data, procedures, and assumptions employed in developing the various estimates are described briefly, and the findings are then discussed in terms of a”preferred” set of estimates. The preferred set of estimates of corrected population for 1970 combines estimates for persons under age 35 based directly on birth, death, and migration statistics, estimates for females aged 35 to 64 based on the Coale-Zelnik estimates (white) for 1950 or the Coale-Rives estimates (Negro) for 1960, estimates for males aged 35 to 64 based on the use of expected sex ratios, and estimates for the population 65 and over based on”Medicare” enrollments and expected sex ratios. These estimates indicate an overall net underenumeration of 5.3 million persons or 2.5 percent in 1970, as compared with 5.1 million or 2.7 percent in 1960, and a net underenumeration of 1.9 percent for whites and of 7.7 percent for Negroes in 1970, as compared with 2.0 percent and 8.0 percent, respectively, in 1960. As in 1960, undercoverage in 1970 was greatest for Negro males (9.9 percent); net error rates exceeded 12 percent in each age group 20 to 49 and reached 17 to 19 percent at ages 25 to 44. All sex-race groups showed marked increases between 1960 and 1970 for children under ten and marked declines at ages ten to 24. Equally reliable estimates of population coverage cannot be prepared for states and smaller geographic units or for the population of Spanish ancestry.     

Confidence intervals for postcensal state population estimates

This paper develops a methodology for constructing confidence intervals around postcensal state population estimates. Using regression equations, forecast intervals are derived around the average age-specific death rates over the postcensal estimation period. These results, combined with the number of postcensal deaths and the most current census counts, are translated into confidence intervals for the age structure. Two approaches are offered for constructing total population confidence intervals. One examines a simulated distribution while the other focuses on the mathematical derivation of population means and variances. The methodology is illustrated by deriving statistically defensible confidence intervals around the July 1, 1975 population of Florida.     

Two hundred years and counting: the 1990 census

On April 1, 1990, the US will take a national census, marking 200 years of census taking in America. A national census has been taken every 10 years in the US since 1790. Mandated by the US Constitution, the decennial census is the basis for reapportionment of the House of Representatives. California, Texas, and Florida are expected to gain the most Congressional seats following the 1990 Census, reflecting above-average population growth in these states. The census also provides important information about the characteristics of the American people, and a growing number of federal, state and local government programs, private corporations, and community agencies use census data. Each census provides a portrait of America, and over the decades these portraits have revealed much about how our country has changed as we have grown from a young agrarian nation of about 4 million people clustered along the Eastern seaboard to a complex post-industrial society of nearly 250 million spread across the continent and beyond. Techniques for taking the census have steadily improved over the past 2 centuries. The 1990 Census will rely heavily on computerization in all its aspects, including field operations, processing, geography, data tabulations, and products. It is likely to be the most accurate census in our history. The 1990 Census is already the subject of a lawsuit, however, charging that minority groups will be counted less completely than the white population. A series of similar lawsuits followed the 1980 Census, but all were unsuccessful. This Bulletin discusses the Census Bureau's plans for taking the 1990 Census, looks back on 200 years of census taking in America, and details such key aspects of the 1990 Census as the questionnaire, census geography and data dissemination plans, census undercount and the homeless.     

Measuring temporal stability in regression models of population estimation

This paper introduces an empirical indicator designed to measure the temporal stability of regression models used to produce subnational population estimates. Analysis of 67 counties in Florida centers on 1970 total population estimates generated from ratio-correlation and difference-correlation models. Comparisons are made between eight different regression specifications and employ a quantitative measure of relative estimate accuracy. The major findings of this study are that (a) variable measurement and type are important determinants of estimate accuracy, and (b) although temporal stability of the coefficients impacts estimation errors, the influence is not as pervasive as is suggested in the literature.     

Evaluation of estimates of underenumeration in the census and the age pattern of mortality,philadelphia, 1880

The schedule of mortality by age for Philadelphia's 1880 population classified by sex and race showed aberrations from Coale and Demeny West, South, and North model life tables. Deviations from standard age patterns of mortality were especially pronounced for the black population. The question addressed in this paper is whether the alternative age patterns of mortality are produced by underenumeration in the 1880 census or by actual variations in the age-specific mortality experience. The conclusion was reached that the underenumeration of the urban population, especially the blacks, exceeds estimates for the national population. In addition, the results indicated that the black population faced risks of dying that genuinely differed from standard age patterns. An attempt to use a Brass logit model to generalize the black mortality experience met with success for females but not for males.     

Some New Techniques for Applying the Housing Unit Method of Local Population Estimation: Further Evidence

The housing unit method of population estimation is often characterized as being imprecise and having an upward bias. In an earlier paper we argued that the method itself cannot be properly characterized by a particular level of precision or direction of bias. Only specific techniques of applying the method can have such characteristics. In that paper we presented several new techniques for estimating the number of households and average number of persons per household (PPH). However, the testing of these new techniques was limited by the lack of census results against which the estimates could be compared. Complete census data on population, households, and PPH are now available and can be used to test alternate estimation techniques. In this paper we replicate the tests reported in our earlier paper using 1980 census data for Florida’s 67 counties. These tests provide further evidence that the new techniques produce more precise, less biased estimates than previously used techniques.     

The completeness of enumeration in the 1973 census of the population of Colombia

The effort is made to determine the true size and distribution by age and sex of the population of the Republic of Colombia in October 1973. After initially arriving at estimates of the levels of fertility and mortality during the intercensal period and then correcting the 1964 census population for age misreporting and selective undernumeration of males, a hypothetical populaiton corresponding to October 1973 is constructed. Comparing the constructed population with the population observed in the census yelds an estimate of completeness of enumeration in 1973 that is relative to the enumeration of females in 1964. This estimate is obtained under the assumption that net international migration during the period was of negligible importance. As there is reason to believe that this is not a valid assumption and upon examining the limited amount of evidence available, speculaitons are made concerning the amount of net out-migration to have occurred during the 1964-1973 period and the size of the coresponding modificaiton in the estimate of completeness of enumeration. After adjusting for underenumeration of males in 1964 and neglecting the impact of international migration, a theoretical 1973 census population of 23,201,000 was estimated. Apart from the total number of people enumerated, the information that was analyzed from the advance sample appears to be of good quality, at least in relation to prior censuses. The estimates of fertility and mortality reveal an important decline in Colombian fertility. By coming up with separate estimates of infant and childhood and adult mortality, it has been possible to shed new light on the shape and the level of mortality in Colombia. The new Brass method for estimating adult mortality provides reliable results even when mortality has been declining, and there are recognizable distortions in the distribution of the population by age.     

An Evaluation of Population Estimates in Florida: April 1, 2000

The housing unit (HU) method is the most commonly used method for making small-area population estimates in the United States. These estimates are used for a wide variety of budgeting, planning, and analytical purposes. Given their importance, periodic evaluations of their accuracy are essential. In this article, we evaluate the accuracy of a set of HU population estimates for counties and subcounty areas in Florida, as of April 1, 2000. We investigate the influence of differences in population size and growth rate on estimation errors; compare the accuracy of several alternative techniques for estimating each of the major components of the HU method; compare the accuracy of 2000 estimates with that of estimates produced in 1980 and 1990; compare the accuracy of HU population estimates with that of estimates derived from other estimation methods; consider the role of professional judgment and the use of averaging in the construction of population estimates; and explore the impact of controlling one set of estimates to another. Our results confirm a number of findings that have been reported before and provide empirical evidence on several issues that have received little attention in the literature. We conclude with several observations regarding future directions in population estimation research.     

Note on the accuracy of local population estimates

Mr. Silcock's article will be of interest to all concerned with local population data. It may be useful to supplement it by a brief account of the fuller examination of the local population estimates made in 1951 by the General Register Office, since this covered all 1472 administrative areas in England and Wales and could be made in more detail than was possible for a private investigator.

Any census, of course, provides information not available, at least in such detail, at other times or from other sources, and also serves as a base from which estimates for succeeding years can be derived. In addition, however, the General Register Office takes the opportunity of a census to try and assess the accuracy of the various types of current population estimates made by the Department. In the case of local administrative areas the comparison of actual and expected populations made after the 1931 Census is discussed in the Text Volume of the Registrar General's Statistical Review for 1930 (pages 100-102).     

Census adjustment and the distribution of federal spending

In 1989, programs that use population counts to determine the distribution of their funds transferred $236 per capita to state and local governments. If the 1990 census were adjusted to reflect undercounting, about 40% of state and local governments would receive increased grants averaging $56 per miscounted person; other jurisdictions would lose an almost equal amount of grant money. The surprisingly small reallocations arise because 1) total funds allocated by population are essentially fixed; 2) allocations depend on other factors in addition to population; and 3) programs vary as to whether they allocate funds in direct or inverse proportion to population.     

Using administrative data to estimate population displacement and resettlement following a catastrophic U.S. disaster

After a large scale evacuation, authorities need to know the new and frequently changing population distributions in order to meet needs for housing, schools, health care, and other services. This paper reviews literature from the fields of demography and other disciplines to identify available administrative data sets that can form the basis of sound, relevant, and timely county-level population estimates following a catastrophic U.S. event. The most appropriate data to estimate population in damaged counties will be disaster-specific data such as housing damage estimates and FEMA applicant counts initially, and later electric accounts and USPS active residences. In heavily damaged counties, data on electric accounts and USPS active residences may not be consistently collected for many months, during which time sample surveys may be needed. For counties that receive an influx of population, school enrollment data provide the most appropriate basis for population estimates. Population estimates for large, heavily damaged counties are highly uncertain. Sensitivity analysis when using estimates for planning in these areas is recommended. The Census Bureau can build on this research by codifying recommendations to local authorities for developing frequent post-disaster population estimates.     

Natural disasters and local demographic change in the United States

Classic studies on local demographic consequences of natural disasters in the United States are now more than 30 years old, raising questions about how and to what extent relevant patterns have changed over intervening years, as the number and cost of recorded environmental hazards have increased. This study examines these questions at the county level for the nation as a whole, using recent census and hazards data in conjunction with statistical methods that account for spatial dependencies among neighboring counties. Results indicate a positive correlation between cumulative disaster impact during the 1990s and changes in local population and housing units; they also reveal patterns of increased socioeconomic polarization among local residents. These findings differ from earlier studies and put recent case studies in broader context, suggesting that current disaster recoveries contribute to the growth of larger and more unequal populations in environmentally hazardous places.     

Some new techniques for applying the housing unit method of local population estimation

The housing unit method of population estimation is often characterized as being imprecise and having an upward bias. We believe that the method itself cannot properly be characterized by a particular level of precision or direction of bias. Only specific techniques of applying the method can have such characteristics. In this paper we discuss several new techniques we have developed for estimating households and the average number of persons per household. Estimates produced by these techniques are compared to estimates produced by several other techniques. Special census results from Florida provide preliminary evidence that the new techniques produce more precise, less biased estimates than the other techniques.     

Coverage of the population in Census 2000: Results from Demographic Analysis

Since the 1960 Census, Demographic Analysis (DA) has been used by the Census Bureau to evaluate the coverage of the population. Administrative statistics on births, deaths, immigration and Medicare enrollments as well as estimates of legal emigration and net undocumented immigration are used to produce demographic analysis estimates of the population for the census date. These estimates are compared to the Census 2000 data to evaluate coverage in the census. The results are also compared to measures of undercount obtained from dual system estimation. The DA measures substantial reduction in net undercount in Census 2000 compared to 1990. The reductions occur among all demographic categories: all broad age groups, males and females, Blacks and Non-Blacks.     

The American Community Survey in counties with “seasonal” populations

The U.S. Census Bureau designed the American Community Survey (ACS) to provide annual estimates of social and economic characteristics for states, counties, municipalities, census tracts, and block groups. Because of its April 1 reference date, in northern nonmetropolitan counties with substantial seasonal population fluctuations the decennial census provides a statistical representation of the demographic and social characteristics of the population at a time when the population is close to its annual minimum. The year-round monthly ACS sample survey has the potential to provide local communities with an unprecedented understanding of the average population characteristics over the course of a year. In the future, the ACS even has the potential for providing social and economic characteristics of the population by season. This paper examines four ACS pilot data collection counties, Oneida and Vilas Counties in northern Wisconsin, and Lake and Flathead Counties in northwest Montana. We hypothesize that the ACS will reflect a resident population over the course of the year that is different from the traditional April 1 decennial census population. While the ACS holds much promise, our research uncovered some sampling problems that are not yet fully resolved. In addition, our analysis was not able to examine ACS estimates for minor civil divisions (MCDs), which are functioning governmental units in many states. The fact that these MCDs often have very small populations, together with the fact that estimated standard errors at the much larger census tract level in these counties are disconcertingly large, raises (currently unanswerable) questions concerning the eventual statistical quality of ACS estimates for small MCDs. Consequently, the adequacy of the ACS as a replacement for the census long form may depend on the ability of the Census Bureau to effectively address the concerns presented in this analysis.     

Plans for the 1970 census of population and housing

The Nineteenth Decennial Census of the United States, covering both population and housing, will be conducted as of April 1, 1970. Planning, testing, and preparatory activities have been underway since early in the decade. Extensive discussions with users of census data led to relatively minor changes in subject content as compared to 1960, but a major increase in the amount of statistics to be tabulated, especially for small geographic areas. For about 60 to 65 percent of the population, the information will be collected through a new mail-out/mail-back system. The rest of the country will be covered by house-to-house canvass. Special efforts to alleviate the serious problem of underenumeration are being undertaken, particularly in the hard-to-enumerate portions of the big cities. The geographic program includes an “address coding guide” through which location identification in most urban areas can be made to specific side of block; this will permit tabulations for new types of small areas. Processing of the data will be performed with the Census Bureau’s Fosdic equipment and advanced computers. Dissemination of the census results will be in the traditional type of printed reports but also, in substantially greater subject and area detail, through magnetic tape, special printouts, etc. To help users exploit the potentialities of the latter material, the Bureau has instituted a “data access” informational program. As in previous censuses, there will be a number of studies to evaluate the 1970 procedures and results.