This week’s release by the Australian Bureau of Statistics of its latest breakdown of Australia’s population estimates (as at 30 June 2006) got good coverage in yesterday’s papers – with variations, of course, for local colour. But none of the stories explained why these numbers are so interesting for psephologists.

Every three years – a year after the first meeting of each new parliament, to be exact – the Australian Electoral Commission studies the latest available population estimates to work out how many seats each state is entitled to in the House of Representatives. (Section 24 of the Constitution sets out the procedure, codified in section 48 of the Commonwealth Electoral Act).

When the AEC last did this, in November 2005, it got the following entitlement for each state: 

New South Wales 49.32
Victoria 36.54
Queensland 28.77
Western Australia 14.61
South Australia 11.23
Tasmania 3.53

That meant, once the fractions were rounded off, that Queensland gained a seat, going to 29, and NSW lost one, dropping back to 49. The other states stayed the same. At the time, it was expected that in the next cycle Queensland would gain yet another seat, and Victoria, perched just above 36.5 quotas, would lose one.

So what do this week’s figures reveal about this? Population growth in
2005-06 averaged 1.3%, ranging from 0.7% in Tasmania to 2.0% in Western Australia. Projecting another two years of growth at the same rates, we get the following entitlements for 2008:

New South Wales 48.57
Victoria 36.57
Queensland 29.44
Western Australia 14.91
South Australia 11.05
Tasmania 3.46

So Victoria is just holding its head above water in terms of keeping its 37th seat, while Queensland is still just short of getting a 30th.

There would be no change at all to the allocation of seats, although New South Wales, with the slowest growth rate of the big states, is in grave danger of losing another one.

Tasmania’s entitlement seems to slip from four to three, but because the Constitution guarantees each original state a minimum of five seats, nothing would change – except that the value of that guarantee, which for years has been a bonus seat, would now be two bonus seats.

So on current trends, the redistributions during the next parliament shouldn’t have to create or abolish any seats.

But population movement is an unpredictable thing, and there’s plenty of time for that to change.