demographics

Demographics is the scientific study of populations, with emphasis on size, structure, and distribution, and how these attributes change over time due to fertility, mortality, and migration.

Key measures include population size, age structure, sex distribution, fertility rates, mortality rates, life expectancy, birth and death rates, and migration flows, as well as indicators of urbanization and population density.

Data are drawn from censuses, vital statistics, surveys, and administrative records. Demographers use methods such as cohort-component projections and life-table analyses, along with population pyramids to illustrate age and sex structure.

Trends include demographic transition from high to low fertility and mortality, aging populations in many regions, rising life expectancy, and increased global mobility. Dependency ratios capture the burden of dependents on the working-age population.

Applications include planning for infrastructure, health, education, and social security; market research and political representation; and monitoring of inequality and development. Limitations include data quality, undercounting, definitional differences, privacy concerns, and potential biases in surveys.