We are delighted to share a ‘DIY’ population forecast graph, created by a few of our very talented supporters. By typing in the percentage change from the current rates of immigration and fertility, you can see for yourself how Australia’s forecast population changes accordingly.
This program is a work in progress and we would like to improve on it over time . If you have experience in programming and would like to help us improve on this program, please feel free to contact us at [email protected]
Further Notes:
How the population changes from year to year depends on five figures. These are the proportion of the population in each age group, the proportion of the women in each age group having a baby, the proportion of people in each age group who die and the net migration of people in this age group in and out of the country. These projections use age groups of one year for all figures – and all are available from ausstats, the statistical website of the Australian Bureau of Statistics. However, there is a delay in releasing the complete set of figures. For example it seems that deaths for the year in each age group may take over a year to be finalised. The projections here are based on 2023 figures. The figures from 2024 should be available soon. The method of putting all these figures together is called the theory of Leslie Matrices.
Small inaccuracies are inevitable – the numbers in each age group in the population change throughout the year and births are not added to the naught year age group nor are deaths subtracted from the other age groups until the start of the next year.
The method depends on tracking female not male fertility as “maternity is the only certainty”.
The outcomes are “projections” not forecasts. They answer the question what would the Australian population be if “this” happened with migration and “that” happened with fertility. The calculations assume that death rates remain constant. The model doesn’t allow much flexibility – only fertility and migration can be changed and they can be changed only once, assuming the change is made at the start of 2025 and applies to all subsequent years.
Notes on the Total Fertility Rate (tfr)
This is calculated by finding the proportion of 15 year old women giving birth (twin births etc are accounted for), add to this the proportion of 16 year old women giving birth, add to this the proportion of 17 year old women giving birth, … and add to this the proportion of 49 year old women giving birth. The total is the number of births that a women would have by the end of her reproductive period if she had each of these birth rates as she progresses through each year of age. One would initially think that for a stable population (in the absence of migration) that this number would have to come out at exactly 2 – each woman on average creates one girl and one boy in her lifetime to replace her family in the next generation. There are factors which mean this initial thought may be quite off target, at least in the short term. The most important factor is the large bulge of young fertile people in Australia at the moment whose baby making much more than counterbalances the numbers of old people ready to die. There are other factors. An obvious one is that some girls and women unfortunately die before they have ever given birth or at least before they have reached the end of their childbearing life. Also slightly more boys than girls are born so a woman has to have on average slightly more than an average of two children so that on average she replaces herself over her lifetime with one girl. The increasing age at childbirth in Australia adds some further complexity so that the tfr may be underestimating the number of children women will actually have as they move towards the end of their reproductive life. This last factor means that with maternal age increasing by about 1 year for every 10 calendar years, the tfr in Australia may actually be underestimating births per woman by 10%. At the moment, ignoring this last factor, the tfr for a long term stable population in Australia in the absence of migration, is about 2.08. Including the last factor would give us an adjusted tfr of 1.89, though making this adjustment is unconventional. Anything more and we expand indefinitely. Anything less and in the very long term we eventually stop population pressure encroaching ever further on the other life forms with which we share this continent.