Last week the Australian Electoral Commission had an interesting media release about the estimated 1.2 million eligible voters that aren’t on the electoral roll. The media release stated:

In the continuing search for 1.2 million Australians missing from the electoral roll, the Australian Electoral Commission (AEC) released information today indicating just who in Australia has the greatest chance of risking their vote in the next election. Electoral Commissioner, Ed Killesteyn explained that Australians aged 18 to 34 years or anyone who has moved house in the last three years, have the greatest likelihood of not being on the electoral roll. “The fact is the younger you are the less likely you are to be on the electoral roll, with young people aged 18-24 years accounting for nearly one third of the 1.2 million eligible Australians missing from the electoral roll,” he said.

So that got me thinking, what would have happened in the 2007 election if those missing from the electoral roll actually enrolled, turned up and voted? Would it have changed the election result — if so, by how much?

First up, we need to look at the AEC estimates of the age breakdowns of this missing 1.2 million odd people.

As we can see, the younger you are the more likely it is that you aren’t on the electoral roll. To show the approximate difference between the actual electoral roll at the 2007 election, and a hypothetical electoral roll where these 1.2 million eligible voters are added, we can take those above numbers as given for their minimum values. For example, we will assume that rather than there being over 370,000 18-24 year olds missing, we’ll assume that there actually is 370,000 18-24 year olds missing. This way, we’ll end up with a conservative estimate – a “if all eligible Australians voted at the election, it would have changed the result by at least this much” type of thing.

Once we combine these numbers with that of the electoral roll in 2007 we get:

This shows what proportion of the electoral roll each age cohort makes up, both at the 2007 election and for our hypothetical “full enrolment” alternative. What we see here is that young people would make up a larger proportion of the voting electorate with our hypothetical “full” electoral roll compared to what we actually had in 2007. 18-24 year olds would be 1.6% larger in weight, 25-34 year olds 0.8% larger — while the older cohorts would make up a smaller weight in voting terms were we to have a a 100% enrolment rate.

This is important, because we know that the younger you are, the more likely you were to vote for the ALP in two party preferred terms in 2007. So would this new age composition of the electoral roll have changed the election result, and if so, by how much?

To start things rolling on the vote projections, we need some good age breakdowns of the two party preferred vote at the 2007 election. Fortuitously, we have arguably the most accurate estimates in the country, by age, of the ALP TPP vote at the last election. You can find the gory details of how it was created over at the top of the Gen Blue post where we first used it (and it’s worth a read if you missed it).

Next up, we need to make an assumption that those people eligible to be on the electoral roll but aren’t, would have voted for the ALP at the same rate, by age cohort, as those who did participate in the 2007 election. That’s not a particularly heroic assumption — but it’s an assumption none the less, so keep it in your thought orbit. I’d be interested to hear anyone’s thoughts on this assumption — as I think those eligible but not enrolled would actually vote for the ALP in slightly higher proportions… but that still works for giving us a conservative estimate.

Once we use our two party preferred estimates by age cohort and apply them to both the 2007 electoral roll and our hypothetical “full” roll, we can determine the two party preferred contribution that each age cohort made to the final two party preferred result.

What we see here, is that the ALP two party preferred result was 52.7% at the 2007 election, but would have been at least 53.1% were the electoral roll “full.

Where the change comes from is the points of two party preferred that each cohort contributes. In 2007 the 18-24’s contributed 6.9 points of the 52.7% final result, but under a full electoral roll scenario they were projected to provide at least 7.9 points — a full 1 point more. That comes about as their contribution is a function of both population size and the relatively high proportion of that cohort that voted ALP. Since their population would be much higher under a “full” roll scenario and they vote ALP at a higher level, they would end up adding more to the ALP two party preferred result under our hypothetical scenario then they did at the actual 2007 election.

You’ll also notice that the older cohorts provide a reduced contribution to the ALP TPP result — that comes about because those cohorts end up being a smaller proportion of the electoral roll once the 1.2 million missing people are added.

Under a hypothetical full electoral roll, the cohorts that vote strongest for the ALP become larger, while the cohorts where the ALP is weakest become smaller — resulting in an overall increase in the ALP two party preferred vote.

A 53.1% two party preferred result would have netted the ALP an additional 4 seats. Yet this is a conservative estimate, we are using minimum numbers here. The actual numbers are higher than we are using — we just don’t know by how much.

The ALP under Rudd is a brutal political outfit — they will wield every conceivable weapon to gain every possible vote at the next election. We should expect some serious voter enrolment programs to be unleashed between now and the next election — simply because of the fact that higher enrollments lead to higher ALP two party preferred vote share, both in terms of the 2007 result as well as the current polling.

In fact, if we use the current polling rather than the 2007 results, even though the ALP is getting a lower primary vote in the younger cohorts than it received at the 2007 election, so is the Coalition — in net terms their respective primary vote losses are nearly all going to the Greens, and flowing back to Labor via preferences. As a back of the envelope calculation, this pushes the potential gain to the ALP from enrolling voters out beyond a minimum 0.4% to well over half a percent of two party preferred.

No party sneezes at a free increase of their vote that’s at least up to 0.5% of TPP, especially when a 0.25% increase is easily attainable by spending some taxpayers cash on enrolment programs.

Expect to be inundated with them.

 Visit Possum’s Pollytics blog for more analysis