Measures of Migration Effectiveness and Their Application to the US Migration System

Abstract

Migration effectiveness is a numerical measure of the degree to which migration is effective in causing population change. Effectiveness is measured as the ratio of net to total (i.e., gross) migration. The measure varies from zero to one. Effectiveness is equal to zero when the numerator, representing net migration, is equal to zero. The two regions exchange migrants, but there is no effect on population change. The maximum value of one occurs when net migration is equal to total migration; in this case all of the migration flows are in one direction, and none are in the other. The measure is sometimes multiplied by 100, to put it on a scale between 0 and 100. In this presentation, a new measure of migration effectiveness is presented. The new measure can be disaggregated into the efficiencies associated with two subsets of destination regions – those with which a region has positive net exchanges, and those with which a region has negative net exchanges. It is applied to the US migration system. Results show that a long period of relatively stable interstate migration flows has been interrupted just twice in the last forty years – once following hurricane Katrina, and once following the onset of COVID-19.