Probabilistic Projections of Urbanization for All Countries

Leontine Alkema, National University of Singapore
Thomas Buettner, United Nations

We describe a Bayesian projection model to produce country-specific projections of urbanization for all countries. The projection model builds onto the United Nations Population Division's current deterministic projection methodology. In the model, the change in proportion urban is projected using the growth rate of the urban-rural ratio, restricted to the population which could become urban in the far future. A time series model describes the annual changes in the growth rate. A Bayesian hierarchical model is used to estimate the parameters of the projection model for each country, based on the country's own urbanization history as well as observed trends in all other countries. A Markov chain Monte Carlo algorithm is used to obtain a sample of future urbanization trajectories. Preliminary results suggest a slower pace of future urbanization compared to the current UN projections for most countries.