In demographic studies, which factor is most likely to contribute to a country's aging population?

The factor that most significantly contributes to a country's aging population is increased life expectancy. When people live longer due to advancements in healthcare, improved living conditions, and better nutrition, the median age of the population rises. As a result, there is a larger proportion of older individuals relative to younger ones.

Countries experiencing increased life expectancy often face challenges related to an aging workforce, the need for more healthcare services, and potential strains on pension systems. This phenomenon is particularly evident in developed nations where high life expectancy accompanies low birth rates, resulting in a demographic shift towards a higher percentage of older adults in the overall population.

High birth rates, low life expectancy, and high immigration rates do not contribute to an aging population. High birth rates typically lead to a younger population, while low life expectancy suggests a decreased number of older individuals. High immigration rates can temporarily alter demographics, but they generally do not address the issue of aging within the existing population unless the immigrants are predominantly older themselves.