Multiple factors can affect changes in societal composition and demographics including fertility, mortality, and migration.

Demographics are a statistical snapshot of a particular point in time, so they do not capture the changing nature of society. In demography, fertility refers to the actual production of offspring, rather than fecundity (the physical capability to produce). Fertility can be measured through a cohort study (following a  subset of the population over time) or through a period study (examining the number of offspring produced during a specific time period). There are a number of different approaches to measuring fertility rate including crude birth rate (CBR), total birth rate (or total fertility rate), and age-specific birth rate. CBR describes the number of live births in a year for every thousand people and is often used as a measure for a particular group’s fertility. Total birth rate describes the average number of children a woman is expected to have over her lifetime. Age-specific birth rate refers to the fertility of women who are a specific age or fall within a range of ages.

Mortality, the death rate within a population, also impacts population size. Mortality rate can be measured in a number of ways. Specific measures of mortality include crude death rate, infant mortality rate, and life expectancy. Crude death rate is the number of deaths per year for every thousand people in a population. Life expectancy measures the number of years that an individual at a given age can expect to live, given present mortality rates. Fertility and mortality rates vary between countries, especially between developing and developed countries. Overall, developing countries tend to have higher mortality rates, higher infant mortality rates, and lower life expectancies. The causes of death also tend to vary between countries. For example, mortality due to malnutrition tends to be much higher in developing countries, whereas in developed countries, people are more likely to die of age-related diseases.

Certain patterns in fertility and mortality occur throughout the world. In developed countries, birth rates typically fall as a society’s economy progresses. In developing countries, economic development can drive population growth. Healthcare advances can lead to a decline in mortality rate as well as an increase in the average age. For fertility, high birth rates have been associated with health impairments and low life expectancy, low living standards, low status of women, and low levels of education. There are claims that as countries go through economic development and social change, birth rate declines. Indeed, demographers consistently find that one of the strongest predictors of fertility rates is women’s educational attainment. Almost universally, higher levels of educational attainment correspond to lower fertility rates. For mortality, developing countries tend to have higher mortality rates, higher infant mortality rates, and lower life expectancies. The causes of death also tend to vary between countries.

Along with fertility and mortality, migration is one of three major variables studied by demographers to measure population change. Migration is the physical movement by people from one place to another; it may be over long distances, such as from one country to another, and can occur as individuals, family units, or large groups. When referring to international movement, migration is generally called immigration.

Lee’s laws divide factors causing migrations into two groups of factors: push and pull factors. Push factors are things that are unfavorable about the area that an immigrant is coming from; pull factors are things that attract the immigrant to the new location. Historically, migration has been nomadic, meaning people sustained movement from place to place over their lifetimes. Although only a few nomadic people have retained this lifestyle in modern times, migration continues as both involuntary migration (such as the slave trade, human trafficking, and ethnic cleansing) and voluntary migration within a region, country, or beyond. Specific types of migrants can include colonizers (who forcefully enter into a country or territory), refugees (who are forced to flee their country), and temporary migrants (who travel to a new place temporarily, such as business travelers, tourists, or seasonal farm workers).

Key Points

• There are a number of different approaches to measuring fertility rate including crude birth rate (CBR), total birth rate (or total fertility rate), and age-specific birth rate.

• Fertility rates are influenced by a number of factors, including intentional measures such as contraception and major social events.

• Demographers have posited a demographic-economic paradox, in which fertility rates decline as countries become more economically developed.

• Almost universally, higher levels of educational attainment correspond to lower fertility rates.

• Like fertility, mortality rate can be measured in a number of ways.

• Specific measures of mortality include the crude death rate, the infant mortality rate, and life expectancy.

• Infant mortality rates measure the annual number of deaths of chldren less than 1 year old per thousand live births.

• Life expectancy measures the number of years that an individual at a given age can expect to live, given present mortality rates.

• Different causes of death become more or less prevalent as countries become more economically developed, and death rates vary between countries.

• Different causes of death become more or less prevalent as countries become more economically developed, and death rates vary between countries.

• Migration is the physical movement by people from one place to another; it may be over long distances, such as from one country to another, and can occur as individuals, family units, or large groups.

• Lee’s laws divide factors causing migrations into two groups of factors: push and pull factors. Push factors are things that are unfavorable about the area that an immigrant is coming from; pull factors are things that attract the immigrant to the new location.

Key Terms

Fertility: The birthrate of a population; the number of live births per 1000 people per year.

Contraception: The use of a device or procedure to prevent conception as a result of sexual activity.

Fecundity: Ability to produce offspring.

Causes of death: The causes of death tend to vary between countries. For example, mortality due to malnutrition tends to be much higher in developing countries, whereas in developed countries, people are more likely to die of age-related diseases.

Life table: In actuarial science and demography, a life table is a table which shows, for each age, what the probability is that a person of that age will die before his or her next birthday (“probability of death”).

Crude death rate: the total number of deaths per year per 1000 people

Seasonal migration: Movement from one place to another generally associated with agriculture and tourism; seasonal agricultural migrants follow crop cycles, moving from place to place to plant or harvest crops.

Emigration: The movement of a person or persons out of a country or national region, for the purpose of permanent relocation of residence.

Immigration: The passing or coming of a person into a country for the purpose of permanent residence.

Push factors: Things that are unfavorable about the area that an immigrant is coming from.

Pull factors are things that attract the immigrant to the new location