  We propose a method for obtaining joint probabilistic projections of
migration rates for all countries, broken down by age and sex. Joint
trajectories for all countries are constrained to satisfy the requirement of
zero global net migration. We evaluate our model using out-of-sample validation
and compare point projections to the projected migration rates from a
persistence model similar to the method used in the United Nations' World
Population Prospects, and also to a state of the art gravity model. We also
resolve an apparently paradoxical discrepancy between growth trends in the
proportion of the world population migrating and the average absolute migration
rate across countries.
