A Decomposition Analysis of Internal Migration Propensity Changes from 1980 to 2015 in Japan

In Japan, while depopulation, aging, and urbanization have caused inter-prefectural migration to decline, net migration to the Tokyo metropolitan area (Tokyo), the Osaka metropolitan area (Osaka), the Nagoya metropolitan area (Nagoya), and the non-metropolitan area (Non-MA) has generally been maintained. The mechanism of this phenomenon is clarified. Using the number of migrants in the Annual Report on Internal Migration in Japan derived from the Basic Resident Registers and the number of people from the Population Census of Japan, out-migration, crude out-migration rate, and standardized out-migration ratio by destination are analyzed, and changes in out-migration are decomposed into demographic and mobility factors. The results show that propensities of inter-metropolitan migration to and from the Tokyo have been increasing, especially from Osaka and Nagoya to Tokyo, and are more pronounced among women than among men. However, migration propensities between Osaka and Nagoya weakened slightly. On the other hand, migration propensities from metropolitan areas to Non-MA declined substantially, whereas those from Non-MA to metropolitan areas were moderate, and those to Tokyo and Nagoya increased or were maintained. In the discussion, first, the mechanism behind the persistence of net migration in the four regions is explored from the viewpoints of migration propensity and the hypothesis of mobility transition. It is argued that while the attractiveness of Tokyo to people from Osaka and Nagoya increased, the attractiveness of Non-MA to people from the metropolitan areas decreased significantly, and that the attractiveness of Osaka relative to Nagoya weakened. In addition, the results shown for Japan are generally consistent with those presented in the hypothesis of mobility transition proposed by Zelinsky. Their association with the socioeconomic context behind the persistence of net migration is discussed. Because Japan's economy has stagnated and local economies of non-MA have been shrinking due to population decline and aging, people are more likely to think that better opportunities exist in Tokyo or Osaka or Nagoya. This could have increased the attractiveness of Tokyo among people in Osaka and Nagoya, and decreased the attractiveness of Non-MA among people in metropolitan areas.