ABSTRACT
Because of births and deaths, every population is subject to a continuous process of renewal to which is given the name replacement. Two ideas which are associated with this process are: the idea of natural increase of a population; and the idea of replacement of generations. The annual rate of natural increase is a global index, very much influenced by the effects of age compositions. The measurement of replacement of generations is carried out with the aid of the net reproduction rate, which, in essence, is an index of cohort analysis. The most elementary way of following the development of a population is to compute the annual increase in its total number. The construction of a period index rests on the composition of a hypothetical cohort, which is subjected to the demographic phenomena being considered with the same intensity as exists in various real cohorts observed during the period studied.
