Slide 26 of 37
Notes:
Actual population is responding to the balance of births and deaths, with a correction in individual countries due to immigration or emigration. Thus
net growth = births - deaths + immigration - emigration
Birth rates and death rates are usually expressed as number per year per thousand of the applicable population. Both are functions of age, so the distribution (the age pyramid) of that population among age groups (cohorts) has an important influence on future trends.
The mortality rate is the probability of an individual of given age dying in the coming year, i.e. it is the death rate for people of that age. It is normally greater for males than for females, i.e. women tend to live longer. This difference is genetically determined. However, more boys are born than girls, so the difference in population is less obvious until the very elderly.