Adjusting the general growth balance method for migration

Abstract

Death distribution methods proposed for death registration coverage by comparison with census age distributions assume no net migration. This assumption makes it problematic to apply these methods to sub-national and national populations affected by substantial net migration. In this paper, we propose and explore a two-step process in which the Growth Balance Equation is first used to estimate net migration rates, using a model of age-specific migration, and then it is used to compare the observed death rates over successive ages against residual estimates made up by the entry rate plus the net migration rate minus the growth rate. This methodology is predicated on the observation that migration rates have a very different age pattern from death rates; it is only when this condition is true that net migration and deaths can be distinguished. The procedure proposed here works reasonably well in populations that generally have good data and rather high net migration rates. There is no reason to prefer the revised migration model over the original Rogers-Castro formulation.