What impact did below-the-line voting have on the 2018 results?

For the last few days I’ve been analysing how preferences flow under the group voting tickets, but of course not every voter votes above the line, and below-the-line votes don’t obey the preference deals.

For today’s post I wanted to examine the question: what impact did those below-the-line votes have on the results of the last election?

The proportion of below-the-line votes was 8.8% in 2018, more than twice the rate in 2010.

As the results come in, Antony Green publishes estimates of who is likely to win, assuming that primary votes then flow as preferences according to each party's ticket. He has helpfully left up these estimates from the 2018 election, which can then be compared to the actual result. The difference between these figures shows the impact of people casting a ballot below the line.

I count three seats which went to a different party in the final result compared to the GVT-only estimate, and in most cases the margins of victory for small parties over larger parties became narrower, if they weren't eliminated entirely.

We don't always have a fair comparison in the final round of the count - perhaps not all preferences are distributed, or a change in the order of elimination means the numbers don't represent the same thing. So I compare the latest stage in the count which is comparable.

I'm going to run through the regions one by one.

In Eastern Metropolitan, Transport Matters still won comfortably, but with 10,000 less votes than in the GVT-only estimate. When there were three candidates left in the count, Transport Matters had about 9,500 less votes, and the Liberal Democrats had about 4,000 less votes, with the Greens holding over 3,500 more votes, but it still wasn't particularly close, with Lib Dem preferences electing TMP easily.

In Eastern Victoria, the result changed, with the Aussie Battler party winning the final seat in the GVT-only estimate. But at the point where there are six parties left in the count, ABP has about 2,900 fewer votes than the estimate, which is about 13% less votes.

The Shooters went on to win this seat. Note that this is the only region where I think the candidates elected would have also won if there were no GVTs.

In Northern Metropolitan, Antony's calculator actually predicted a fourth win for Derryn Hinch's Justice Party at the expense of the Liberal Party, who had polled 0.988 quotas of primary votes but received literally no above-the-line preferences.

It wouldn't have taken much leakage for the Liberal Party to win, but the Hinch party's chances were particularly hurt by a large share of the Reason vote being cast below the line. Just 53.7% of Reason voters cast an above-the-line vote, which is by a long distance the lowest rate in the state. Presumably most of those below-the-line votes were for Fiona Patten, so it wasn't a problem for her election, but when she had a surplus it didn't flow as predicted. But it's also the case that the Liberal vote was slightly higher at the key point in the count than it would have been with GVTs-only, while the Reason surplus was much smaller.

In Northern Victoria, the Liberal Democrats won the third seat and Derryn Hinch's Justice party won the fourth seat. Labor and Coalition had each polled just short of two quotas - Labor scraped across the line for the fifth seat and the Coalition missed out, but it was much closer than it would have been without below-the-line votes.

When the Liberal Democrats were elected, their surplus was 7107 votes less than in a GVT-only scenario. This meant they had a lot fewer votes to pass on to the Hinch party. Labor also polled over 3000 more votes, and the Coalition polled more votes too, meaning the gap between the Hinch party and the unsuccessful Coalition candidate shrunk from 25,000 votes to about 11,000 votes.

In South Eastern Metropolitan, Antony's calculator gave the final seat to Transport Matters, but this didn't end up happening. At a key point in the count, Transport Matters were knocked out before the Greens. If they outlasted the Greens, the Greens vote would have mostly flowed to Labor, and the Labor surplus then pushed Transport Matters ahead of the Liberal Democrats. Instead, Transport Matters were knocked out and the Liberal Democrats benefited from that Labor surplus.

In Southern Metropolitan, the comparison is straightforward. The final match-up for the final seat was between Sustainable Australia and the Greens in both scenarios, but the margin of victory was significantly slimmer in reality.

The Greens had approximately ten times as many primary votes as Sustainable Australia, so the latter was far more reliant on preferences from other parties - and below-the-line votes from those parties rarely flowed in the same way as ticket votes. A slightly higher below-the-line rate would have likely seen the Greens hold on to their seat.

In Western Metropolitan, the race for the final seat was between Derryn Hinch's Justice Party and the Democratic Labour Party. The DLP was leading, but Labor was elected to the fourth seat and their surplus elected the Hinch party.

The race was much closer in reality, with a margin of 4,466, compared to a margin of 10,830 if all votes were above the line.

In Western Victoria, the final seat was won by Animal Justice, beating the second Liberal candidate after receiving Greens preferences.

The margin for Animal Justice over the Greens was 21,324 if all votes were above the line, but this margin shrank to 12,474 in reality.

It's not clear who would've won if the AJP had been knocked out - quite a lot of AJP votes came from centre-left parties and would have likely favoured the Greens, but perhaps not as strongly as Greens preferences favoured Animal Justice over the Liberal Party.

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