Box 7: Population Projections

Box 7: Population Projections

The accompanying graph shows projected growth in Tasmania's population according to the Australian Bureau of Statistics 'high', 'medium' and 'low' variant assumptions, 2008 (respectively Series A, B, and C). The Series B projections are considered the most likely scenario and are used for most comparative purposes (e.g. comparisons by state or nation).

When considering data projections it is extremely important to understand what they do and do not indicate. They are not forecasts, but rather, indications of what the population size and composition will be if (and only if) the underlying assumptions about births, deaths and migration prevail.

Typically a number of 'variants' or scenarios are calculated, but the ABS publishes only three - these are known as the high (Series A), medium (Series B) and low (Series C) variants, or sometimes, the best-case, medium-case, and worst-case scenarios. For Tasmania they show the outcome of:

* (Series A - the 'high variant' scenario): a rise from the current birth rate of 2.2 to 2.31 by 2022, then remaining constant; from 2011 a constant annual net migration gain of 2,760 (comprised of 1,000 net interstate migration and 1,760 net international migration); and life expectancy continuing to improve at a constant rate, by around one year of life for every ten projected.
* (Series B - the 'medium case' or 'medium variant' scenario): a fall by 2021 to a slightly lower birth rate (2.08); from 2010 a constant average annual net migration gain of approximately 940 (comprised of a net loss of 500 interstate migrants and a net gain of 1,440 international migrants): and life expectancy continuing to increase, but at a decelerating rate.
* (Series C - the'low variant'): a fall by 2022 to a substantially lower birth rate (1.85) and, from 2011, an annual net migration loss of 880 (comprised of a net interstate loss of 1,120 and a net international gain of 2,000) than at present. Life expectancy is the same as for the medium variant.

Although the Series A projections indicate the possibility of growth to 770,000 by mid century, it should be understood that this is highly unlikely. The annual net migration assumption of 2,760 per year has only been surpassed on six occasions in the past 107 years (with four of those occasions in the immediate WW2 post-war period, when Australia and Tasmania welcomed large numbers of post war migrants). Similarly the Series A birth rate of 2.3 births per woman, while only a little above that at present, has not been observed in Australia or any counterpart countries since the 1960s. Accordingly it is highly improbable that the Series A assumptions or growth indicated under them will 'come true'.

By comparison, the Series B assumptions are plausibly within reach. Net migration gains of 950 have been observed 23 times in the past 107 years, but more importantly, four times in the past five years. However the average for the past ten years is in fact only 31 persons, so the Series B migration assumptions may be a little on the high side. Against that, the birth rate assumption of 2.08 births per woman is fractionally below that of the present, and may well endure; Tasmania has always had earlier childbearing and larger completed family sizes than elsewhere in Australia (with the exception of the Northern Territory).

The Series C assumptions are also plausibly within reach in that the migration assumption of -880 per year has been met on numerous occasions. However the average for the past ten years is (as noted above) +31, and for the past twenty years, -352, so it would take a significant shift in the migration stakes to see Tasmania experience a consistent annual net loss of the magnitude indicated. The Series C birth rate, on the other hand, was experienced in Tasmania in the mid 1980s, the late 1990s and the early 2000's, and could well return to that level after the present large cohort (the children of the baby boomers) have completed their childbearing.

ABS population projections are typically re-run every two years. Those used in the graphs on this web site were calculated in 2008 and will be updated when new data are released.

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