Age-structure changes are an intrinsic feature of the demographic transition from high mortality and fertility to low mortality and fertility. Initially, the demographic transition increases the share of the working-age population, creating opportunities for economic boosts through demographic dividends. Particularly some Asian countries have benefited greatly from such demographic dividends in the past. Overtime, however, the demographic transition leads to population ageing, which brings various implications for economies and societies worldwide. In Asia, many countries are ageing rapidly, while others continue to maintain a relatively young age structure. These differences may also be related to migration. Migration is also often discussed as a possible policy response to counteract population ageing. This thesis identifies global patterns in changes in the share of working-age population and examines associated demographic factors. With a specific focus on Asian countries, it assesses the impact of migration on population ageing in the past and its potential impact in the future. All analyses in this thesis are based on data from the United Nations’ World Population Prospects 2022. First, past, present and projected age-structure changes are analyzed in the context of demographic dividends, covering 148 countries worldwide. Cluster analyses are conducted to identify patterns of age-structure changes between 1950 and 2100, while linear regression models are used to detect associations between these changes and relevant demographic factors. Second, the impact of migration on past age-structure changes is assessed for the period 1990-2020 in 51 Asian countries using decomposition analysis. An existing decomposition approach is extended to incorporate the concept of prospective age, which accounts for differences in life expectancy when assessing population ageing. Third, the potential impact of migration on population ageing between 2022 and 2050 is analyzed in eleven Asian countries by adopting the United Nations’ replacement migration concept. In this analysis, both chronological and prospective indicators of population ageing are applied.

The results underline the heterogeneity of global age-structure changes in the course of the demographic transition. This underscores the need to take into account a country’s specific demographic development when assessing its potential for a demographic dividend. The experience of some Asian countries, where rapid fertility declines in the past have been followed by sharp increases in the share of the working-age population, is only one of several global patterns. Differences in age-structure changes are associated with differences in fertility, but also with migration and population momentum – two factors that have so far received relatively little attention in the discussion of demographic dividends. Focusing on Asian countries, this thesis reveals that differences in population ageing across countries are at least partly driven by migration. However, the volume of migration potentially required to offset population ageing over the next decades seems unrealistically high in most countries. The results emphasize that migration can play a role in age-structure changes, but population ageing can barely be halted by immigration alone. Thus, comprehensive policies seem to be a key factor in ensuring further development in ageing countries in Asia and beyond.