Uncertainty variants of population forecasts

Abstract

When using population forecasts it is important to take into account the degree of uncertainty of the results. For that reason the Netherlands Central Bureau of Statistics publishes low and high variants next to the most probable medium variant. In the low variant fertility and net immigration are low and mortality is high. In the high variant the opposite applies. The width of the interval between the variants is based on an analysis of previous forecast errors. The degree of uncertainty of the various forecast results turns out to vary strongly. The low and high variants are based on the same deterministic cohort-component model that is used for the medium variant. Hence the probability that the interval between the variants covers the true value is unknown. On the basis of a statistical time-series model of forecast errors of total population growth, a confidence interval of total population size can be estimated.