What are demographic concepts?

The basic demographic concepts used of demographers are crude birth rates, fertility, fecundity and crude death rates.

Crude birth rates are usually expressed as the number of live births per year per 1000 of the population. They are called crude rates because of their very general character. Crude birth rates, for example, do not tell us what proportion of a population is male or female, or what the age-distribution of a population is (the relative proportions of young and older people in that population).

Where statistics are collected that relate birth or death rates to such categories, demographers speak of specific rather than crude rates. For example, age-specific death rates specify the proportions of a population dying per year in each age-group.

Birth rates are an expression of the fertility of women. ‘Fertility’ refers to how-many live-born children the average woman has. A fertility rate is a complex calculation. It is the number of children that would be born to an average woman in a given population if she were to live to the end of her child bearing years, and Bear children at the same rate as those currently in the age- group who have Just passed the age of childbearing.

Fertility is distinguished from fecundity, which means the number of children women are able to have in biological, terms. It is physically possible for a normal woman to bear a child every year during the period she is capable of conception.

There are variations in fecundity according to age of puberty and menopause (both of which differ on average between countries, as well as among individuals). While there may be families in which a woman bears twenty or more children, fertility rates in practice are always much lower than fecundity, because social and cultural factors limit breeding.

Crude death rates (also called mortality rates) are calculated as the number of deaths per 1000 of population per year. Again there are major variations between countries; but death rates in many third world societies are falling to levels comparable to those in the West.

Like crude birth rates, crude death rates only provide a very general index of mortality (the number of deaths in a population); specific death rates give more precise information. A particularly important aspect of death rates in general is the infant mortality rate.

The infant mortality rate is the number of babies that die before the age of one per 1000 live-births in any year. One of the key factors underlying the population explosion has been the reduction in infant mortality rates.

Declining rates of infant mortality are the most important influence on increasing life expectancy that is the number of years the average person can expect to live. While life expectancy has increased in most societies in the world, life span has remained unaltered. Only a tiny proportion of people live to be a hundred or more