Moving up and down the urban hierarchy: Age‐specific internal migration patterns in Japan based on the 2020 census.

This study aimed to understand the age‐specific internal migration patterns in Japan where more than a quarter of the population is aged ≥65 years and the national population is on the decline, focusing on the urban hierarchy. Demographic efficiency, which is the ratio of net to gross migration, was calculated for each migration flow between the levels of urban hierarchy in Japan based on the 2020 census. The results showed that the overall upward migration, which is a movement from lower to higher levels in the urban hierarchy, was dominant. A variation in migration patterns by age confirmed that young adults, especially those aged 20–24 years, moved up the urban hierarchy unidirectionally, while people of preretirement and retirement age moved down. The older adults (aged 75 and over) were inclined to move up. Regarding sex‐based differences, the demographic efficiency of women was higher than that of men. Additionally, the upward movement of women was predominant in almost all age groups. These findings suggest the possibility that aggregated migration behaviours may vary by sex, which has received little attention in previous migration studies focusing on urban hierarchies in other countries. Furthermore, this study discussed policy implications based on the observed patterns, such as the impacts of older adults' migration on social security at each hierarchy level and a possible relationship between women's upward migration patterns and future fertility decline. [ABSTRACT FROM AUTHOR]