Describe the factors that can affect the size of a country's population.

The size of a country's population at any time depends on the balance among three forces: births, deaths and migration. Population grows when births plus immigration exceed deaths plus emigration, and falls when the reverse holds.

1. Birth rate (fertility). The number of live births per \( 1{,}000 \) people per year. A high birth rate, encouraged by early marriage, large-family cultures, low use of family planning and high infant mortality that prompts more births, raises population size.
2. Death rate (mortality). The number of deaths per \( 1{,}000 \) people per year. It is influenced by medical facilities, nutrition, sanitation, standard of living, war, famine and epidemics. Falling death rates enlarge the population.
3. Migration. Immigration (movement into the country) increases the population, while emigration (movement out) decreases it; net migration is the difference between the two.
4. Natural increase. The excess of births over deaths; a wide gap means rapid natural growth.
5. Government policy. Policies that promote or discourage childbearing, control immigration, or improve health care alter the size of the population.
6. Age and sex structure and marriage patterns. A large proportion of people in the reproductive age group, and a balanced sex ratio, raise the potential number of births.

Examination reminder: reduce the whole answer to one identity: \[ \text{Population change} = (\text{Births} - \text{Deaths}) + (\text{Immigration} - \text{Emigration}) \] then explain what drives each term.