An evaluation of population projections by age

Area of Science:

• Demography
• Population Studies
• Statistical Modeling

Background:

• Previous research focused on total population projection accuracy, neglecting age-specific demographic forecasts.
• Accurate age-group population data is crucial for various planning and policy applications.
• Subnational (state, county) population projections require distinct accuracy assessments.

Purpose of the Study:

• To evaluate the precision and bias of age-group population projections at national, state, and county levels.
• To compare the accuracy of projections generated by complex versus simplified cohort-component methods.
• To identify patterns in projection errors across different age strata and geographic scales.

Main Methods:

• Analysis of age-group population projection accuracy using national, state (US), and county (Florida) data.
• Comparison of projections from full cohort-component models versus simplified versions.
• Assessment of projection bias and precision over varying time horizons.

Main Results:

• Age-group error patterns diverge between national and subnational projections.
• Projection errors vary considerably among different age groups.
• Disparities in age-group errors diminish with longer projection horizons.
• Methodological complexity showed no consistent effect on projection precision or bias.

Conclusions:

• Subnational population projection accuracy is highly age-dependent and differs from national trends.
• Simplified demographic projection methods may be as accurate as complex ones for certain applications.
• Understanding age-specific error patterns is vital for improving demographic forecasting at all geographic levels.