Probabilistic County-Level Population Projections.

Population projections provide predictions of future population sizes for an area. Historically, most population projections have been produced using deterministic or scenario-based approaches and have not assessed uncertainty about future population change. Starting in 2015, however, the United Nations (UN) has produced probabilistic population projections for all countries using a Bayesian approach. There is also considerable interest in subnational probabilistic population projections, but the UN's national approach cannot be used directly for this purpose, because within-country correlations in fertility and mortality are generally larger than between-country ones, migration is not constrained in the same way, and there is a need to account for college and other special populations, particularly at the county level. We propose a Bayesian method for producing subnational population projections, including migration and accounting for college populations, by building on but modifying the UN approach. We illustrate our approach by applying it to the counties of Washington State and comparing the results with extant deterministic projections produced by Washington State demographers. Out-of-sample experiments show that our method gives accurate and well-calibrated forecasts and forecast intervals. In most cases, our intervals were narrower than the growth-based intervals issued by the state, particularly for shorter time horizons.

Probabilistic population forecasting: Short to very long-term.

Population forecasts are used by governments and the private sector for planning, with horizons up to about three generations (around 2100) for different purposes. The traditional methods are deterministic using scenarios, but probabilistic forecasts are desired to get an idea of accuracy, assess changes, and make decisions involving risks. In a significant breakthrough, since 2015, the United Nations has issued probabilistic population forecasts for all countries using a Bayesian methodology that we review here. Assessment of the social cost of carbon relies on long-term forecasts of carbon emissions, which in turn depend on even longer-range population and economic forecasts, to 2300. We extend the UN method to very-long range population forecasts by combining the statistical approach with expert review and elicitation. While the world population is projected to grow for the rest of this century, it will likely stabilize in the 22nd century and decline in the 23rd century.

Super Aging in South Korea Unstoppable but Mitigatable: A Sub-National Scale Population Projection for Best Policy Planning.

This research portrays the spatial and temporal progression of super-aging in regions throughout South Korea. Using a single-year population projection considering gross domestic migration, this research identifies which regions will shortly become a super-aged society. A cohort-component method with a migrant pool model is applied. The county-level national population registration data (2000-2018) are aggregated into 37 regions for the model run. In 2020, 16 rural regions will become super-aged societies. By 2029, all 37 regions, including the metropolitan areas, will join the group, with Sejong, the administrative capital, being the last to enter. In brief, the rural areas become super-aged earlier than the metropolitan areas, and within a decade, those 65 years old or older will make up the majority of the national population. Among all the metropolitan areas, Busan, the largest harbor city, will be the first to be super-aged in 2023. Sejong will experience the most radical change between 2020 and 2050. The research outcomes demonstrate that demographic changes in the rural and metropolitan areas are different; hence, the recent population policies, such as promoting fertility, may not work in the rural areas as they have already lost their population momentum due to the extreme and ongoing urbanization throughout the nation. The unstoppable aging will pose adverse effects on future citizens (who are mostly senior) both financially and medically. An increase in health care expenditure and a nationwide blood shortage for transfusion are anticipated, for example.

Future Interstate Highway System Demands: Predictions Based on Population Projections.

The Interstate Highway System (IHS) used to be a symbol of American growth and its economic machine, but the IHS has not been expanded much since its inception. Recently there are both executive and legislative desires to restore and upgrade the IHS to its role as a premier system that can meet the growing and changing demands of the twenty-first century. Demographic forecasting is a precursor to rational transportation planning and decision activities. This paper provides population projections into 2060 at the county level for the entire US using cohort-component methods. We found that the US is projected to experience population growth across all age groups over the next 50 years. The projected growth, however, varies across the entire US. Population growth areas are in the west/south/east border states and the Atlanta-NC-Nashville triangle. Population decline areas include many counties from the northeast corner to the Appalachian region, counties bordering the five Great Lakes, counties along the Mississippi River, the Deep South states, and Alaska. We also identified the counties that may need additional or less transport capacity based on projected population change and proximities to IHS. We further identified the counties with high population density but without the IHS network that are projected to experience rapid population growth. IHS demands will be affected by the aging population, the young population, baby boomers, millennials, immigrants, telecommuting, and autonomous vehicles. This study provides the necessary demographic forecasting for decision and policy makers in better deciding whether and where to expand or invest in the IHS when the resources become available.