When the ALP recently floated the idea of allowing 16 and 17 year olds to vote, the thing that struck me was, firstly, how so many Greens were in favour of the idea and secondly, how so many Libs opposed it.

Being a cynic and believing that even with the cute and cuddly Greens, 90% of politics is driven by pure vested interests – I thought it might be worth having a look at how this would play out by electorate.

The problem was getting an estimate of the number of 16/17 year olds in each electorate. The last robust piece of data we have on this is the 2006 census, which unfortunately is now 3 years old. However, if we just look at how the situation would have played out at the 2007 election with an expanded electoral roll, our age data from 2006 – the data that we’ll use to expand the roll – would only be 12 months old.

So what we need to do is look at the number of 15 and 16 year olds in each electorate at the Census in 2006 and use that as our estimate for the maximum number of 16 and 17 year olds in each seat at the election in the following year of 2007.

The first thing that stood out when the data started to be chewed was the large negative correlation between the Greens primary vote in each electorate and the number of 16-17 year olds. If we hypothetically expand the electoral roll to contain all 16-17 year olds in each seat, and then look at the proportion of the voting population in each seat those 16 and 17 year olds would have made up – we can run a scatter plot (and regression line) of the that proportion against the Greens primary vote.

greensyoung

What this tells us is that as the proportion of 16-17 year olds in each electorate increased, the Greens primary vote decreased. The electoral demography here is pretty simple – the Greens do well in places with few high school children because their vote is primarily situated in inner city seats rather than the middle and outer suburbs.

If we assume that only 50% of 16 and 17 year olds would have voted, and let us also assume that the Greens would have done well with this age cohort and received 30% of the vote – if we look at how that would have increased the Greens primary vote and compare that hypothetical increase against their actual vote achieved at the election, we get:

greenhypo

The seats where the Green vote would have increased the most are in the places where their vote is the lowest – but the increases here are small, less than 1%. We can see that by looking at the distribution of the hypothetical increase in the Greens primary vote.

greendist

In those inner city seats where the Greens need an extra 4 or 5% to give them a chance of beating the Liberals into second place and riding to victory over Labor off Liberal preferences, the 16-17 year old age cohort really doesn’t bring anything to the table for the simple reason that there isn’t enough of them in those seats.

Where the Greens would have benefited was in the public funding stakes – although by not as much as one might think.

Using the same assumptions as above, the Greens would have gained an additional 83,450 voters. At the public funding rate at the 2007 election of 210.027 cents per vote- that adds up to an additional $175,268 that would have been delivered into the Greens bank account.

While an expansion of the electoral roll would have benefited the Greens, it wouldn’t have done so in any meaningful way in the seats where they need it the most and would have provided only a modest financial benefit. The real benefit to the Greens of expanding the electoral roll would probably be in the Senate, especially in those cases where the Greens are fighting it out for the final Senate spot in each state and a few thousand votes starts to seriously matter.

UPDATE:

Pure Poison has an interesting post about the motivations of each side of politics when it comes to their respective positions on lowering the voting age.

UPDATE 2:

Since this is getting coverage wider than the usual nerdset, it’s worth pointing out something that Ben in comments mentioned.

The above just looks at the estimated Greens vote in isolation – if we also bring in the vote the ALP would receive among any 16-17 year olds, the beneficial effects for the Greens in lower house seats would get completely wiped out. The gains to the Greens would only be financial and in the Senate.