The population of countries may differ, but they all tend to be included in three general models of age and gender:
1- Increased growth: It is characterized by the presence of greater proportions of the population in the younger age groups.
2- Slow growth: It is characterized by the presence of smaller proportions of the population in the younger age groups.
3- Steady or diminishing growth: It is characterized by the presence of equal numbers of the population in almost all age groups, and gradually decreasing in the older age groups.