Geographical pattern analysis of income migration in the United States

Most of the research on internal migration has focused on the determinants of migration. Considerably less work has focused on migration impacts. A significant impact of internal population movement is its ability to effect income redistribution. While much work in regional economics and regional science has been carried out on income distribution and redistribution, the tools of the population geographer have not been employed to study 'income migration'. How one conceptualises the impacts of migration depends on whether one takes the viewpoint of aggregate area-level income change, of per capita change, or of longer-term (future earnings) change. Several empirical analytical measures are proposed in order to conceptualise the various income impacts of migration. An income version of the demographic effectiveness ratio commonly employed in migration research is suggested. A procedure is set forth for splitting total state-level income change into components attributable to (a) net migration, and (b) the income differential between in-and out-migrants. Another decomposition procedure is developed for examining how the changes in per capita income of states reflect three different income differentials: those between (a) in-migrants and 'stayers', (b) out-migrants and 'stayers', and (c) in-migrants and out-migrants. Examination of these measures, and of typologies based on them, highlights how income migration significantly and differentially impacts upon US states. The methods are illustrated here in the context of an important new American data source: the 1993-94 migrant income data released by the US Internal Revenue Service.