Federal redistributions in Australia rely on two sets of numbers – the actual enrolment numbers at the time that the process commences, and an estimate of how many voters will be enrolled at a future point, about three and a half years after the conclusion of the process. While electorates need to be drawn within 10% of the average enrolment at the start of the process, the projected numbers are far more important, since seats need to be drawn within 3.5% of the average on those figures.
These projected numbers ensure that electorates are drawn so that faster-growing seats have smaller populations, and slower-growing seats have larger populations, and thus population change reduces malapportionment, rather than increasing it.
Unfortunately, if those projected numbers are no good, the whole thing is undermined.
The projected figures for the Victorian federal redistribution were released in October, and I posted about them here.
There have been a number of people raising concerns about those figures in the comments, and earlier this week the AEC acknowledged the issue, saying that “The AEC has been informed by the ABS that there was an error in the initial enrolment projections supplied for use in the redistribution of Victoria.” They have now released this corrected data, and it does change the distribution of population in a way that will favour outer suburban growth areas, which will be drawn with smaller electorates than if the original projections had been used.
I haven’t personally investigated the problem with the projected numbers, but as an example Zac Gross posted this graph, showing that almost all Victorian SA1s were assumed to have growth of almost exactly 10%, whereas in other redistributions the growth rates vary (as you’d expect).
First up, I’ve modified the following table that I posted in October which breaks down electorates in Melbourne into different parts of the city north and south of the Yarra River, and breaks rural Victoria into east and west.
The original projections had the 26 seats of Melbourne collectively about three-quarters of a seat under quota, but that deficit was spread out across the city. The 16 seats south of the Yarra were about half a seat under quota, while the 10 seats north of the Yarra were about a quarter of a seat under quota. It was particularly surprising that the six seats of western Melbourne, an outer suburban area where you’d expect fast growth, was projected to barely gain any population relative to other parts of the state. This looked very different to the trends in the NSW redistribution, where Western Sydney is set to gain a seat while the eastern half of the city loses two.
But this picture looks different with the new figures. The ten seats north of the Yarra are pretty much spot on quota, although the central city seats are under quota and will probably need to expand to take in surplus growth in the western suburbs. The 16 seats south of the Yarra are now 84% of a seat under quota, rather than 50%. Indeed the eight seats I defined as “eastern Melbourne” are almost half a quota under themselves.
This makes a huge difference to the implications for the redistribution. It’s now clear that the seat to be abolished will be in the eastern suburbs of Melbourne.
This doesn’t mean that other areas won’t be affected – overall the seats north of the Yarra (urban and rural) fall short of their quota by 17% of a seat. It’s possible this deficit could be spread out amongst the 19 seats on the north side and thus doesn’t require a seat to cross the Yarra, but there will definitely be a need to distribute population differently within that area.
Another way to look at the figures is via this map. It has two layers. The first shows the revised projected quotas for each seat, while the second shows how much each seat’s projected quota was changed by the revisions.
The first map now makes a lot more sense. Most seats in Victoria are under quota (as you would expect when a seat has been abolished), but the outer suburban fringe on the north-west and the south-east both tend to be over-quota. This was not the case on the original figures.
When you toggle to the second tab, it’s very clear that the new projections have favoured outer suburban areas.
La Trobe, Lalor and Calwell were all projected to be under quota but are now projected to be well over quota. The change in La Trobe was 13.2% of a seat’s population!
It’s quite unfortunate that this mistake was made after the first two rounds of submissions, which would have been made based on those projections being correct. The mapmakers will be able to use the correct figures, but will be relying on public submissions based on entirely different numbers. But I’m not sure the alternative of allowing further rounds of public submissions would have been viable. At least the problem has been identified and fixed. It would have been far worse to continue with incorrect numbers, that would have likely led to fast-growing outer suburban areas being under-represented.
Western Australia was also affected by this issue, and I’ve got a blog post coming up covering WA this afternoon.