The gross and net reproduction rates differ only on account of the mortality factor and the difference, at present, is quite appreciable. If we are investigating the possibilities of increased reproductivity we would naturally study the causes of the difference between these rates and the likelihood of that difference reducing and thus increasing the reproductivity. In this paper we will determine the extent to which this difference is caused by mortality in different age groups and mortality due to different causes.

In a paper by the present writer (J.I.A. Vol. LXXV, p. 151) the rates of mortality for Australia for different ages and different causes of death were determined. The same material will be used in the present analysis where, assuming constant (1938) fertility and using 1935 mortality, we shall determine the difference between the gross and net reproduction rates and the extent to which this difference results from mortality at different ages and from various causes of death. It should be emphasized here that the many arguments raised against any analysis based on causes of death (transfers between causes, variations in diagnosis, selecting a single cause from multiple causes, etc.) do not apply with much force to the causes of death at the ages that are, in this problem, of most interest.