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	Migration Effectiveness Index	Net Migration Rate
分野	Migration Studies	人口学
系統	Process / pipeline	Process / pipeline
提唱年	2002	1976
提唱者	Martin Bell and colleagues	Classical vital-statistics measure (formalized by Shryock & Siegel)
種類	Descriptive index of migration efficiency and impact	Rate of net population change due to migration per unit population
原典	Bell, M., Blake, M., Boyle, P., Duke-Williams, O., Rees, P., Stillwell, J., & Hugo, G. (2002). Cross-national comparison of internal migration: issues and measures. Journal of the Royal Statistical Society: Series A, 165(3), 435-464.	Preston, S. H., Heuveline, P., & Guillot, M. (2001). Demography: Measuring and Modeling Population Processes. Blackwell. ISBN: 9781557864512
別名	Migration Efficiency Index, Aggregate Net Migration Rate, ANMR, MEI	Net Migration Ratio, Crude Net Migration Rate, Net Migration per 1000
関連	3	4
概要	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.	The net migration rate expresses the net effect of migration on a population's size as a rate: net migration — in-migrants minus out-migrants over a period — divided by the population at risk, conventionally stated per 1000 people. It is the migration counterpart to the rate of natural increase and a standard component of population accounting. Because directional migration flows are often poorly recorded, net migration is frequently not counted directly but estimated as a residual from the demographic balancing equation or by comparing surviving cohorts across two censuses.