From Masculinisation to Feminisation of Metropolitan Areas: The Changing Impact of Internal Migration on Regional Sex Ratios in Japan

In Western countries, more women live in urban or high-population-density areas than men, reflecting selective rural-to-urban migration by sex. In contrast, the sex ratio of the Tokyo metropolitan area, which includes the capital in Japan, is relatively high compared to other areas within the country, suggesting male-dominant migration towards that area. However, there were contradictory patterns of recent migration, such as selective migration of women to metropolitan areas and a larger net in-migration of women to metropolitan areas than men. This can be interpreted to mean that the role of internal migration changed from increasing the sex ratio of metropolitan areas through ‘masculinisation’ to decreasing it through ‘feminisation.’ This study investigates the changes in migration patterns and their impact on the regional sex ratio in Japan using macro-level data. It first shows the distinctive feature of high sex ratios of inter-prefectural migrants and migration rates from 1958 to the present. The sex ratio increased until approximately 1990 and decreased thereafter. Subsequently, gender differences in education and employment were summarised as factors related to migration patterns by sex. These differences have gradually become smaller. Finally, this study quantifies the impact of inter-prefectural migration on prefectural sex ratios using four decennial censuses from 1990 to 2020. The results indicated that the impact of migration changed from ‘masculinisation’ to ‘feminisation’ of the Tokyo metropolitan area and vice versa in the case of nonmetropolitan areas in about 2010. This suggests that the migration patterns in Japan have gradually resembled those of Western countries over the past three decades.