Population Glossary

Age-sex structure
The composition of a population as determined by the number or proportion of males and females in each age category. The age-sex structure of a population is the cumulative result of past trends in fertility, mortality, and migration. Information on age-sex composition is essential for the description and analysis of many other types of demographic data.

Baby boom
A dramatic increase in fertility rates and in the absolute number of births. In the United States this occured during the period following World War II (1946-1964).

Birth rate (or crude birth rate)
The number of live births per 1,000 population in a given year. Not to be confused with the growth rate.

Death rate (or crude death rate)
The number of deaths per 1,000 population in a given year.

Growth rate
The number of persons added to (or subtracted from) a population in a year due to natural increase and net migration; expressed as a percentage of the population at the beginning of the time period.

Less developed countries
Less developed countries include all countries in Africa, Asia (excluding Japan), and Latin America and the Caribbean, and the regions of Melanesia, Micronesia, and Polynesia.

Life expectancy
The average number of additional years a person of a given age could expect to live if current mortality trends were to continue for the rest of that person's life. Most commonly cited as life expectancy at birth.

More developed countries
More developed countries include all countries in Europe, North America, Australia, New Zealand, and Japan.

Mortality
Deaths as a component of population change.

Net migration
The net effect of immigration and emigration on an area's population in a given time period, expressed as an increase or decrease.

Population pyramid
A bar chart, arranged vertically, that shows the distribution of a population by age and sex. By convention, the younger ages are at the bottom, with males on the left and females on the right.

Rate of natural increase
The rate at which a population is increasing (or decreasing) in a given year due to a surplus (or deficit) of births over deaths, expressed as a percentage of the base population.

Zero population growth
A population in equilibrium, with a growth rate of zero, achieved when births plus immigration equal deaths plus emigration. Zero growth is not to be confused with replacement level fertility.