Using Australian records of human births for the first six decades of the twentieth century, the proportions of male and female births are studied in relation to the mother's age, the father's age, the parents' ages in combination, and certain other factors. The principal data used relate to the years 1931–55, during which over 3 million children were born, yet even so the significant features are not easy to discern.

From statistics on Australian confinements during the period 1944–63 it seems that the following conclusions can legitimately be drawn.

The decline in the number of legitimate live births in England and Wales from the peak in 1964 has been partitioned into components due to changes in fertility rates, components due to changes in the composition of the population exposed to risk, and an interaction component. Fertility rates specific for age of mother at birth of child, duration of marriage, parity and age of mother at marriage were considered but in all cases it was found that the decline was not (...) as great as the change in fertility rates implied. This was due to increases in the number of births due to changes in the composition of the population exposed to risk. (shrink)