In this research, the trends in mortality, fertility, and growth rate of the population in Iran during the years of 1921-86 have been studied. This period coincides the first stage of demographic transition in Iran. Thus, in order to have a better understanding, the demographic trends
in Iran in terms of the theory of demographic transition have been taken into consideration.
Due to the lack of reliable statistical data, the appropriate demographic measures have been inferred from the stable models. In the process of fitting the defective demographic data to the models, the historical information, comparative statistics, and sociological insights
have not been disregarded.
On the basis of the transition theory, it may be concluded that
during the first stage of transition:
- The level of mortality gradually declined.
- The level of fertility remained relatively constant.
- The rate of population growth increased.
The findings of this research conform the following expectations:
- The expectation of life at birth has increased; from almost twenty five years in 1921 to nearly sixty years in 1986.
- According to the estimation, the birth rate was about forty three per thousand per year circa 1921 and it was almost the same (43.3) in the decade of 1976 - 86. Therefore, regardless of the minor and gradual changes during the years of 1921 - 86, as it was theoretically expected, the level of fertility remained relatively constant.
- As a result of the increasing gap between the declining level of mortality and the relatively constant level of fertility in these years, the natural growth rate increased; from five per thousand per year circa 1921 to about thirty two per thousand per year in the, decade of 1976-1986.
In the end, it has been tried. to decompose the increased population of Iran, according to the demographic components of growth, ie., fertility, mortality, and migration. As it was expected, the changing level of mortality was the main factor causing the growth of population in Iran during these years. In fact, the contribution of this factor to the formation of the increased populatin was about 82.4% in 1921 and, regardless of migration, it increased to 96.2% in 1986.