The Accuracy of Population Projections

Population projections are key elements of many planning or policy studies, but are inherently inaccurate. This study of past population projection errors provides a means for constructing confidence intervals for future projections. We first define a statistic to measure projection errors independently of the size of the population and length of the projection period. A sample of U.S. Census Bureau and U.N. projections indicates that the distribution of the error statistic is relatively stable. Finally, this information is used to construct confidence intervals for the total population of the United States through the year 2000

Changes in Adult Smoking Behavior in the United States: 1955 to 1983

A new method for analyzing data from two surveys, applied to questions on smoking in the Current Population Survey and the Health Interview Survey, shows that the net rate at which adults have been quitting smoking has increased in the last three decades. Two periods, the late 1960s and the late 1970s, had especially high rates. Quit rates are higher for older people and males but not markedly so for whites. The number of light and moderate smokers has been decreasing, but the number of heavy smokers has been increasing

Advances in Mathematical Models for Population Projections

Population projections are simply extrapolations of demographic patterns that have remained constant in the past into the future. This observation by Keyfitz simultaneously provides a philosophical base for forecasting techniques and sets off a search for demographic patterns. We begin with a discussion of the reasons for disaggregate projections, how the reasons effect data requirements, and how models relieve the strain. The next section discusses advances in demographic models, especially extensions of the relational methods developed by Brass. Finally, we discuss how time-series models, in conjunction with model patterns, can be used to make forecasts with appropriate confidence intervals. The paper motivates the techniques through examples of Swedish life tables, and describes appropriate mathematical properties for projection models

A Note on the Population 50 Years Hence

Attitudes toward societal planning horizons may assume that there is relatively little overlap between the population of today and the population of the future. To test this assumption a rough calculation is made of how many people who are alive today will be alive 50 years hence. The calculation is made on the basis of 3 age cohorts for a sample of 10 countries from 8 demographic categories. While the result is uncertain because of changing mortality, poor data, etc., the authors believe it is reasonably robust. About forty percent of those alive today will be alive in 50 years. This proportion includes 550 million people 15 or older. These results suggest that long planning horizons are rational from the point of view of the self-interest of the existing population. Further research into societal planning horizons would be useful

An Analysis of Indirect Mortality Estimation

This paper investigates the robustness of the Brass child-survivorship indirect mortality estimation technique. It develops an analytical method for studying the error or bias caused in indirect mortality estimates by poor data, badly chosen model functions, and specific demographic assumptions that are often violated in practice. The resulting analytical expressions give insight into the rationale of indirect methods, the conditions under which they are robust, and the magnitude of errors that occur when specific assumptions are violated

On the Relationship of Childhood to Labor Force Migration Rates

Based on stable population theory, a formula is derived relating childhood migration rates to adult migration rates. A simple approximation of this formula is tested on Swedish migration data and is found to work well. The reasons for its failure in some instances are also explored

The Accuracy of Population Projections

Although population studies are key elements of many planning and policy studies, they are inherently inaccurate. This report attempts to measure the inaccuracy through a comparison of past projections with the actual population figures. The aim of this historcal study is not to criticize or applaud the quality of previous demographic predictions, but rather to provide confidence intervals for projections made today. This should allow planners to use projections more objectively by providing a range of reasonable possibilities rather than a single estimate

Estimating Age-Specific Transition Rates for Population Subgroups from Successive Surveys

As an extension of a recent result in generalized stable population theory, this paper develops a new method for estimating age-specific transition rates for population subgroups based on data from two successive surveys. A test based on detailed data on smoking behavior from the 1976 and 1981 censuses of New Zealand shows that the method works well when the data are aggregated into a small number of irregular age groups and when the surveys are irregularly spaced

An Analysis of Indirect Mortality Estimation

For some years, IIASA has placed considerable emphasis on both population studies and methods of analysis and estimation. These two strands of research are combined in this report, which develops an analytical method for the derivation of errors in estimations based on indirect data, and illustrates this method by applying it to Brass's child survivorship estimation technique. The method described here makes it possible to study the sensitivities of estimates to the underlying assumptions, and provides algebraic expressions that are both more general and easier to interpret than computer results. These expressions give some insight into the rationale of the indirect methods, the conditions under which they are appropriate, and the possibilities of correcting the effects of inappropriate assumptions