The study of methods of measurement of the rate of population growth is one of the most fundamental aspects of demographic science and one which, from its nature, should be of particular interest to the actuarial profession. It is therefore fitting that this paper should be devoted to a discussion of this side of the subject, particularly in view of the importance which the analysis of population trends has assumed in modern times as the result of the decline in birth-rates experienced by this country in common with most of the leading civilized nations.
Leaving out of account losses and gains by migration, the future development of a given population is determined by the numbers of children that people have, the proportions of these who survive and the sizes of the families which they have in their turn, the cycle continuing indefinitely. Whilst the consequences of changes in mortality must not be underestimated it is clearly the wide possible range of variation in birth-rates which plays by far the more important part in shaping future population trends. The measurement of population growth therefore rests largely on the analysis of fertility, a subject of considerable complexity.