Basic demographic processes and their characteristics

Fertility is the natural capability to produce offspring. As a measure, "fertility rate" is the number of offspring born per mating pair, individual or population. Fertility differs from fecundity, which is defined as the potential for reproduction (influenced by gamete production, fertilization and carrying a pregnancy to term). A lack of fertility is infertility while a lack of fecundity would be called sterility.

Human fertility depends on factors of nutrition, sexual behavior, culture, instinct, endocrinology, timing, economics, way of life, and emotions.

Crude birth rate (CBR) - the number of live births in a given year per 1,000 people alive at the middle of that year. One disadvantage of this indicator is that it is influenced by the age structure of the population.

General fertility rate (GFR) - the number of births in a year divided by the number of women aged 15–44, times 1000. It focuses on the potential mothers only, and takes the age distribution into account.

Age-specific fertility rate (ASFR) - The number of births in a year to women in a 5-year age group, divided by the number of all women in that age group, times 1000. The usual age groups are 10-14, 15-19, 20-24, etc.

Total fertility rate (TFR) - the total number of children a woman would bear during her lifetime if she were to experience the prevailing age-specific fertility rates of women. TFR equals the sum for all age groups of 5 times each ASFR rate.

The expectation of life (or life expectancy) - the number of years which an individual at a given age could expect to live at present mortality levels.

The replacement level fertility – the average number of children a woman must have in order to replace herself with a daughter in the next generation.

Infertility primarily refers to the biological inability of a person to contribute to conception. Infertility may also refer to the state of a woman who is unable to carry a pregnancy to full term. There are many biological causes of infertility, including some that medical intervention can treat.

The rate of natural increase – is the crude birth rate minus the crude death rate of a population. Usually developing countries have a positive or high natural increase rate. Developed countries have a negative/neutral or low natural increase rate, but many developed countries have their population due to immigration despite their negative RNI.

Mortality rate is a measure of the number of deaths (in general, or due to a specific cause) in a population, scaled to the size of that population, per unit of time. Mortality rate is typically expressed in units of deaths per 1000 individuals per year; thus, a mortality rate of 9.5 (out of 1000) in a population of 1,000 would mean 9.5 deaths per year in that entire population, or 0.95% out of the total.

One distinguishes:

· The crude death rate, the total number of deaths per year per 1000 people.

· The perinatal mortality rate, the sum of neonatal deaths and fetal deaths (stillbirths) per 1000 births.

· The maternal mortality ratio, the number of maternal deaths per 100,000 live births in same time period.

· The maternal mortality rate, the number of maternal deaths per 1,000 women of reproductive age in the population (generally defined as 15–44 years of age).

· The infant mortality rate, the number of deaths of children less than 1 year old per 1000 live births.

· The child mortality rate, the number of deaths of children less than 5 years old per 1000 live births.

· The age-specific mortality rate (ASMR) - This refers to the total number of deaths per year per 1000 people of a given age (e.g. age 62 last birthday).Р

Note that the crude death rate as defined above and applied to a whole population can give a misleading impression. The crude death rate depends on the age (and gender) specific mortality rates and the age (and gender) distribution of the population. The number of deaths per 1000 people can be higher for developed nations than in less-developed countries, despite life expectancy being higher in developed countries due to standards of health being better. This happens because developed countries typically have a completely different population age distribution, with a much higher proportion of older people, due to both lower recent birth rates and lower mortality rates. A more complete picture of mortality is given by a life table which shows the mortality rate separately for each age. A life table is necessary to give a good estimate of life expectancy.

Migration refers to the movement of persons from a locality of origin to a destination place across some pre-defined, political boundary. Thus demographers do not consider tourists and travelers to be migrating.

Different types of migration include:

· Seasonal human migration mainly related to agriculture and tourism to urban places

· Rural to urban, more common in developing countries as industrialization takes effect (urbanization)

· Urban to rural, more common in developed countries due to a higher cost of urban living (suburbanization)

· International migration

Net migration rate is the difference of immigrants and emigrants of an area in a period of time, divided (usually) per 1,000 inhabitants (considered on midterm population). A positive value represents more people entering the country than leaving it, while a negative value means more people leaving than entering it.