Should Population Projections Consider "Limiting Factors"--and If So, How?

Forecasting International Migration in Europe: A Bayesian View

“…To avoid extremities, a reasonable level of control of the limiting factors should be exerted, depending on various dimensions (demographic, social, economic, environmental, and cultural) of the forecasting context, as well as on the scale of the predictions (Cohen, 1998). Examples of applications of models successfully taking into account various constraints of the socio-demographic setting include Massey and Zenteno (1999), as well as Cohen et al (2008).…”

A Guide to Global Population Projections

“…Long-term global population projections − and most projections over shorter terms or smaller regions − do not project vital rates based on formal models of how these rates may be related to socioeconomic factors. Trends in socioeconomic factors are thought to be harder to predict than the demographic processes themselves (Keyfitz 1982), and relations between demographic and other variables are not generally considered well known enough to quantify reliably (Cohen 1998). The best known example of an attempt to formulate a comprehensive, causal model of demographic processes is the World3 model that served as the basis for the Limits to Growth study in the early 1970s (Meadows et al 1971).…”

“…Future agricultural systems, energy supplies, and water availability are difficult to foresee in their own right, and there is no consensus in these areas to which demographers might turn. Third, even if these factors could be reliably predicted, their effects are mediated through economic, political, and cultural systems in ways that are not possible to quantify with confidence (Cohen 1998). Thus, even projections contingent on projected developments in other areas would be highly uncertain.…”

“…Although no long-term projections routinely take carrying capacity into account, some researchers (Cohen 1998, NRC 2000 have argued that it may be worth considering limiting factors when projecting population, especially over long time horizons, in particular locations where resources are especially limiting and potential for trade is low, or when the intention is to warn against an undesirable outcome, to describe a path to a desirable state, or to analyze the consequences of some hypothetical relationship between demographic factors and constraints. Lutz et al (1996) examined the potential demographic consequences of an assumed carrying capacity of 2.5 billion for Sub-Saharan Africa as an illustration of how such an exercise might be carried out.…”

What if fertility decline is not permanent? The need for an evolutionarily informed approach to understanding low fertility

“…Doing this, however, highlights the fact that a new set of assumptions-or better, an actual predictive theory about the evolution of fertility in human populations-are not readily available to supplant the current set of assumptions [6]. On balance, evolutionary and ecological approaches to population change are under-represented in population projection specifically (but see [22,23]), and in the study of fertility change in low-fertility contexts generally [24]. Interdisciplinary collaboration and appreciation of multiple approaches-including evolutionary theory-will be needed to develop alternative population projections in the future [6].…”