Population change is a result of fluctuations in birth rates, death rates, and migration.

The Demographic Transition Model (DTM) presents changes in birth and death rates over time. It suggests that death rates fall before birth rates leading to population expansion. However, DTM isn't universal. For instance:

• England, Wales, and Sweden, where the DTM was first observed, had a longer timescale than many LEDCs (Less Economically Developed Countries).
• Ireland's DTM was influenced by emigration and rising death rates due to the famine (1845-9).
• Japan saw population expansion before World War II, followed by contraction when expansionist plans couldn't be met.

Natural Increase: Difference between birth rate and death rate, represented as a percentage. When the death rate is higher, it results in a natural decrease. This measure does not account for migration.

Population change: Considers birth rate, death rate, and migration.

Doubling time: Number of years needed for a population to double in size. It's calculated by dividing 70 by the rate of natural increase (expressed in years).

Population momentum: Tendency for population to grow even with a fall in birth rate or fertility levels. It happens due to a high concentration of people in their pre-childbearing and childbearing years.

Population projections: Predictions about future population trends based on fertility, mortality, and migration patterns.

Total Fertility Rate (TFR): Average number of births per thousand women of childbearing age. It represents completed family size if fertility rates remain

Status of Women: High birth rates are common in countries where women's status is low and female education and employment rates are low. For example, in Singapore, as women's status improved alongside socio-economic changes, TFR fell from 3.0 in 1960 to 0.81 in 2015.

Education & Ambition: More educated parents generally have fewer children. Middle-income families with high aspirations but limited resources often have smaller families. On the other hand, people with limited resources or ambition might have larger families due to a lack of perceived alternatives.

Location of Residence: Rural areas tend to have higher fertility rates due to social pressures on women, less state control, and limited opportunities for women. Urban areas like shanty towns also have high fertility rates due to their youthful population structure.

Religion: Religions generally promote large families and oppose birth control. However, in HICs (High-Income Countries), adherence to religious beliefs on fertility varies. For instance, Italy and Spain, both Catholic countries, have low birth rates.

Health of Mother: Healthy women are more likely to have successful pregnancies, but women who suffer from health issues might become pregnant more frequently due to higher rates of infant mortality and unsuccessful pregnancies.

Economic Prosperity: Economic prosperity can increase the birth rate. On the contrary, increased costs, recession, and unemployment often lead to a decline in the birth rate, partly due to the high cost of raising children. In the UK, it was found that the cost of bringing up a child could exceed $300,000.

Need for Children: High infant mortality rates can result in increased pressure to have more children, known as replacement or compensatory births. In agricultural societies, larger families might be preferred for farm labour and security in parents' old age.

Life expectancy: Average number of years a person is expected to live, assuming that demographic factors remain constant. It varies across countries due to factors like poverty, conflict, and disease prevalence (like AIDS).

Some HICs expect over 50% of those born in 2007 to live past 100 years. This can be attributed to better food supply, clean water, and housing. However, increased life expectancy does not guarantee good health in later years, with many elderly people suffering from various physical and mental health issues.