Migration Effectiveness Index
The migration effectiveness index measures how efficiently the gross churning of people between regions actually redistributes population, by expressing net migration as a share of total migration turnover. Two regions can each exchange enormous numbers of migrants and yet end up with almost unchanged populations, because the inflows and outflows nearly cancel; the same net change could instead arise from a small, lopsided, highly directed flow. The effectiveness index distinguishes these cases: it runs from near zero, where gross flows are balanced and population is barely redistributed, toward one hundred, where migration is so one-directional that almost every move contributes to net change. Martin Bell and colleagues codified this measure in their influential 2002 framework for cross-national comparison of internal migration, alongside companion indices of overall migration intensity and the aggregate net migration rate, which combines intensity and effectiveness into a single summary of how much migration reshapes the settlement pattern. Together these indices form a standard toolkit for describing and comparing migration systems across countries and over time.
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