Decomposing the Drivers of Population Aging: A Research Note.

Population aging is an important and increasingly relevant area of study for demographers. A growing body of research seeks to determine how long-term changes in births, mortality, and migration-the three drivers of any demographic process-have shaped the present aging situation. Using variable-r decomposition and cohort data, this research note presents a formula for the change in the old-age dependency ratio to determine the extent to which relative changes in births, as well as in mortality and migration rates, contribute to aging. This perspective provides a careful and in-depth picture of aging and contributes to the debate concerning whether changes in births or mortality have had the strongest effect on population aging. When applied to Australia, the United States, and several European populations, the decomposition of the old-age dependency ratio shows that aging occurred in all populations and that changes in both births and mortality contributed to this aging. Analysis of these populations demonstrates that although they differed regarding which of these factors contributed more, changes in births prevailed as the more significant factor. In nearly all populations, migration decreased the rate of population aging.

National Population Growth Rate, Its Components, and Subnational Contributions: A Research Note.

A population's current growth rate is determined jointly by changes in fertility, mortality, and migration. This overall growth rate is also the average of age-specific growth rates, which can be decomposed into the result of historical changes in fertility, mortality, and migration. However, doing so requires more than 100 years of historical data, meaning that such analyses are possible only in a select few populations. In this research note, we propose an adapted version of the variable-r model to measure contributions to the population growth rate for countries with shorter demographic series. In addition, we extend this model to explore the contribution of subnational changes to the national population growth rate. Our results demonstrate that the age-specific growth rates obtained from short historical series, say 25 years, closely match those of the longer series. These abbreviated age-specific growth rates closely resemble the growth rate at birth of their respective cohorts, which is the major determinant of population growth, except at older ages where mortality becomes the main explanatory element. Exploring subnational populations, we find considerable heterogeneity in the age profile of the components of growth and find that the most populous regions tend to have an outsized impact on national-level growth.

The Components of Change in Population Growth Rates.

The demographic balance equation relates the population growth rate with crude rates of fertility, mortality, and net migration. All these rates refer to changes occurring between two time points, say, t and t + h. However, this fundamental balance equation overlooks the contribution of historical fertility, mortality, and migration in explaining these population counts. Because of this, the balance equation only partially explains a change in growth rate between time t and t + h as it does not include the contribution of historical population trends in shaping the population at time t. The overall population growth rate can also be expressed as the weighted average of age-specific growth rates. In this article, we develop a method to decompose the historical drivers of current population growth by recursively employing the variable-r method on the population's average age-specific growth rates. We illustrate our method by identifying the unique contributions of survival progress, migration change, and fertility decline for current population growth in Denmark, England and Wales, France, and the United States. Our results show that survival progress is mainly having an effect on population growth at older ages, although accounting for indirect historical effects illuminates additional contributions at younger ages. Migration is particularly important in Denmark and England and Wales. Finally, we find that across all populations studied, historical fertility decline plays the largest role in shaping recent reductions in population growth rates.

Efectos de la migración sobre el crecimiento poblacional a largo plazo de las provincias cubanas / Efeitos da migração sobre o crescimento populacional de longo prazo das províncias cubanas / Effects of migration on long-term population growth in the provinces of Cuba

Cuba es un país que, además de presentar niveles de fecundidad inferiores al nivel de reemplazo, ha registrado un significativo saldo migratorio negativo. Se observa también un intenso flujo migratorio interno cuyo patrón es muy diferente entre las provincias. Debido a la magnitud de estos flujos migratorios, la migración se presenta como un componente demográfico importante en la dinámica poblacional cubana. De esta forma, el objetivo de este trabajo es estimar el efecto de la migración interna e internacional sobre el potencial de crecimiento a largo plazo de Cuba y de sus provincias. Para esto, calculamos medidas de reproducción y de crecimiento poblacional a partir de los métodos demográficos convencionales y de la metodología propuesta por Preston y Wang (2007), que se basa en los métodos de variable r. Considerando el patrón demográfico corriente, en la mayoría de los territorios de Cuba se observa una reducción substantiva en la capacidad de reposición de las generaciones y en tamaño futuro de la población cuando se consideran los efectos de la migración.

Cuba é um país que, além de apresentar níveis de fecundidade inferiores ao nível de reposição, tem registrado um saldo migratório líquido negativo significativo. Observa-se também um intenso fluxo migratório interno, cujo padrão é bastante diferente nas diversas províncias do país. Devido à magnitude destes fluxos migratórios, a migração apresenta-se como um componente demográfico importante na dinâmica populacional cubana. Assim, o objetivo deste trabalho é estimar o efeito das migrações interna e internacional sobre o potencial de crescimento de longo prazo de Cuba e de suas províncias. Para tanto, foram calculadas medidas de reprodução e de crescimento populacional a partir dos métodos demográficos convencionais e da metodologia proposta por Preston e Wang (2007), que se baseia nos métodos da variável-r. Levando em conta o padrão demográfico atual, observa-se, na maioria dos territórios de Cuba, uma redução substantiva na capacidade de reposição das gerações e no tamanho futuro da população quando se consideram os efeitos da migração.

Cuba has shown very low fertility levels, even below replacement level, in addition to significant negative net migration flows. In the country's interior there is intense population mobility, characterized by different migration patterns from one province to another. In this article the effects of both internal and international migration flows on long-term population growth in Cuba and in its provinces are discussed. We estimate reproduction and population growth measures using conventional demographic methods, together with the methodology developed by Preston and Wang (2007), based on variable-r methods. Given current demographic patterns in the majority of Cuban provinces, and when migration effects are accounted for, our analysis shows significant negative consequences for the future maintenance of the Cuban population.