A massive field of 16 candidates have nominated for the upcoming Wentworth byelection, making the distribution of preferences crucial in deciding the winner.

The Liberal party looks likely to suffer a huge swing against it, but preference flows and the peculiarities of our voting system could still see its candidate, Dave Sharma, hold on, depending on who makes it to the final round of vote counting.

Recent polling suggests the Liberal vote in Wentworth has dropped below 40%. By my count, there are four potentially viable candidates who could threaten the Liberals, or who could have a sizeable share of the preferences: independents Kerryn Phelps and Licia Heath, Labor’s Tim Murray and the Greens’ Dominic Wy Kanak.

The order of elimination of candidates isn’t usually that important. Two candidates stand out clearly in the lead (usually Labor and Liberal), and then the preferences of all minor candidates are distributed to find a winner.

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This byelection won’t be like that. We don’t know which candidate will come second on primary votes, and there’s a real possibility that the candidate who comes second on primary votes could be knocked into third place by minor-candidate preferences.

Under our preference system, the lowest-polling candidate is first eliminated, with their votes distributed. This process is repeated until someone reaches a majority of the vote. This process makes it possible for someone to leapfrog another candidate on preferences and survive until a later round.

A Reachtel poll (commissioned by GetUp) from 17 September put Kerryn Phelps in second place on 21%, followed by Labor on 15% and the Greens on 12.6%. On these numbers, it’s entirely plausible that either Phelps or Labor could make it to the final round of the count (with the Greens not out of contention). The Liberal party’s Dave Sharma is polling at only 36%, so whoever wins would do so only with a large number of preferences from other candidates.

The same poll put Labor’s two-party-preferred vote at 48%, down from 50% in an earlier poll. Labor certainly has a chance of winning from these numbers, but it’s not very comfortable.

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There’s reason to believe Phelps would do better from Labor preferences than Labor would do from her preferences. Labor voters are less likely to consider preferencing the Liberal party, while Phelps’s voters may be less committed to voting against the Liberals. On this basis it’s reasonable to assume Phelps would do better than Labor’s 48%, likely putting her in the lead on a Phelps vs Sharma two-candidate-preferred count.

In a close race, you could imagine Phelps would gain enough preferences to defeat Sharma, but Labor would not, so Sharma’s survival could depend on which candidate reaches the final count.

Considering how these preferences are likely to flow, the Liberals could well be hoping Labor stays in the top two, reducing the anti-Liberal preference flow and giving them a better chance to hold on.