Application of a probabilistic framework to New Zealand's official national population projections

This paper reports on the application of a probabilistic forecasting framework to Statistics New Zealand’s 2004-based national population projections. The assumptions of the Series 5 projections (the middle series)were set as the medians of the fertility, mortality and net migration predictive distributions, and a combination of time series models and judgement was used to generate the distributions. Particular attention was paid to the forecasting of international migration. A model was designed that made use of the official total net migration assumption but provided separate age-sex-specific immigration and emigration inputs to the cohort component model, thus overcoming a number of theoretical and practical limitations of forecasting with age-sex-specific net migration. The resulting probabilistic population forecasts suggest that New Zealand’s demographic future is considerably uncertain. The forecasts indicate an 80 per cent probability that the population will lie between 4.41 and 5.07 million by 2026 and between 4.48 and 5.88 million by mid-century. Copyright © 2005 Population Association of New Zealand