An Extension of Migration Effectiveness Indices: Accounting for the Impact of Migration on Population Structure

ABSTRACT This study introduces the age‐weighted migration effectiveness index (AWMEI), a new metric that integrates age‐specific variation into a single measure of migration effectiveness. Traditional indices, such as the migration effectiveness index (MEI) and age‐specific MEI (ASMEI), effectively address the first aspect of migration effectiveness—population redistribution—but overlook the second aspect—transformation of the composition of regional populations. The AWMEI bridges this gap by weighting net migration flows according to their age structure, offering comprehensive insights into migration's dual impacts. Applied to South Korea's internal migration data (2001–2022), the AWMEI uncovers patterns previously obscured by conventional measures. Nationally, an increasing divergence between AWMEI and MEI reveals growing age disparities in migration patterns. At regional and local scales, the AWMEI highlights substantial age‐specific population shifts even where traditional indices indicate minimal migration effectiveness. Amid broader spatial demographic transitions, the AWMEI provides a robust analytical framework for capturing migration's demographic implications. Its inherent adaptability further allows broad application across diverse dimensions of population composition and various research contexts.