Sub-national stochastic population projections with highly volatile international migration: the case of New Zealand

Michael Cameron, University of Waikato
Jacques Poot, University of Waikato

Cross-border population mobility is globally increasing in level, complexity and volatility. National population projections can account for growing uncertainty in levels and variability of international migration by adopting a probabilistic framework. However, international migration is strongly spatially selective, affecting some regions (predominantly metropolitan) more than others. Probabilistic sub-national population projections therefore ideally combine spatially-varying degrees of uncertainty with respect to international migration, with endogenous – but relatively more stable – patterns of internal population redistribution. The present paper considers the case of New Zealand, which has had in recent years the highest immigration and emigration rates, and the greatest variability in population growth among OECD countries. Probabilistic population projections are generated for territorial authorities within the Waikato region. Internal and international migration are considered separately. Assumptions are informed by demographic trends and regional-level expert consultation. The results are compared to official sub-national projections obtained with the conventional cohort component methodology.