Demographic concepts and indicators

Demographers use a few key indicators to describe a population:

• Birth rate and death rate: births or deaths per 1000 people in a year. The growth rate = birth rate minus death rate.
• Replacement level: the birth rate at which each generation just replaces itself, so the population stays the same.
• Fertility rate: live births per 1000 women aged 15–49 (the child-bearing ages). Age-specific fertility rates, for each age group, are more precise.
• Total fertility rate (TFR): the average number of children a woman would have in her lifetime.

Two indicators show poverty and poor health care especially clearly:

• Infant mortality rate: deaths of babies before their first birthday, per 1000 live births.
• Maternal mortality rate: deaths of women in childbirth, per 1,00,000 live births.

Sex ratio: the number of females per 1000 males. Nature produces slightly more boys than girls at birth, yet in a normal population the ratio is about 1050: girls resist disease better in infancy, and women live longer than men. So a ratio well below 1000, as in India, points to social bias against girls and women.

Age structure: the share of people in each age group: children, working-age adults and the old.

Dependency ratio: the number of dependents (under 15 and over 64) compared with the working-age group (15–64). A falling dependency ratio means more workers for every dependent. That can give a demographic dividend: a boost to growth, because more people are earning and saving.

But the dividend lasts only for a time: as today's workers grow old, the ratio rises again.