Dynamics of internal migration rates in Japan: Declining trends disaggregated by age, period, and cohort

In recent decades, a long-term internal migration decline has been observed in many countries, including Japan. To explore the dynamics of internal migration in Japan, we apply the age-period-cohort-interaction model to five-year inter-prefectural migration rate data from six nationally representative surveys conducted between 1991 and 2016. The results show regular age-specific migration patterns, fluctuating period effects, and inter- and intra-cohort differences. Age effects reflect general migration patterns and largely explain the decline, while period effects show no consistent trend. Relatively recent generations tend to exhibit statistically significant high or low migration rates, visible as inter-cohort differences. While some of these inter-cohort differences converge with age, cohorts that experienced socio-economic shocks in their early 20s display consistently low migration rates. This pattern indicates that such shocks impose long-term structural constraints to migration as a pathway to accessing improved employment, suggesting the need for targeted policy interventions to counter declining internal migration.