An Overview of Population Projections—Methodological Concepts, International Data Availability, and Use Cases

Abstract

Population projections serve various actors at subnational, national, and international levels as a quantitative basis for political and economic decision-making. Usually, the users are no experts in statistics or forecasting and therefore lack the methodological and demographic background to completely understand methods and limitations behind the projections they use to inform further analysis. Our contribution primarily targets that readership. Therefore, we give a brief overview of different approaches to population projection and discuss their respective advantages and disadvantages, alongside practical problems in population data and forecasting. Fundamental differences between deterministic and stochastic approaches are discussed, with special emphasis on the advantages of stochastic approaches. Next to selected projection data available to the public, we show central areas of application of population projections, with an emphasis on Germany.

Migration Forecasting—Significance and Approaches

“…Another critical point when selecting a model for migration forecasting is the incorporation of uncertainty, with deterministic or stochastic approaches being the main distinction [7]. Most migration (and population) projections are deterministic [43].…”

“…However, they suffer from several limitations, including the missing quantification of future developments by probabilities. We do not intend to go into this in more detail; interested readers are referred to a more detailed discussion on this in [7]. Stochastic approaches are preferable, as they not only allow uncertainty to be incorporated into the forecasts but can also cover autocorrelations and cross-correlations in the different migration variables [5] (e.g., the correlation between immigration and emigration or correlations between the immigration of different age groups).…”

“…Time series data are not always available with sufficient length and consistency, however. Moreover, even reliable time series data may not always be representative of the future development if, for example, extraordinary events have occurred in the past which will (almost) certainly not be repeated in the future [7]. In the European experience, for instance, there has been a significant change in the opportunities of cross-border migration over time.…”

“…The three main drivers of national population forecasting are fertility, mortality, and international migration, with the latter being special in the sense that it is the most volatile demographic component [5] and is significantly influenced by sudden events, such as violent conflicts, which are themselves in many cases unpredictable [5,6]. Since population forecasting is an indispensable basis for planning in, for example, economics, infrastructure, health, education, or social insurance [7], sound migration forecasting approaches are of considerable importance. Therefore, users of migration projections (regarding the distinction between forecasts and projections, see, for instance, [7]) should be well aware of their respective assumptions and accompanying limitations.…”

“…Since population forecasting is an indispensable basis for planning in, for example, economics, infrastructure, health, education, or social insurance [7], sound migration forecasting approaches are of considerable importance. Therefore, users of migration projections (regarding the distinction between forecasts and projections, see, for instance, [7]) should be well aware of their respective assumptions and accompanying limitations. Our contribution aims to present and discuss different approaches for readers who are unfamiliar with the practice of migration forecasting.…”