When I had my first Super Saturday article published on Thursday May 31, I asked myself this question: “Who will win the Super Saturday by-elections?”. The answer I gave was a series of probability statements, which look pretty good in the light of the results on July 28. Consequently I have decided on the same approach for the forthcoming Wentworth by-election on October 20.

I give the Liberal candidate Dave Sharma a 55% chance, the Independent Kerryn Phelps a 35% chance and the Labor candidate Tim Murray a 10% chance. I’ll now explain the concepts behind those figures, beginning with the assertion that Sharma will enjoy a big lead on first preference votes. However, either Phelps or Murray can win after the distribution of preferences. The only certainty is that Sharma’s preferences will not be distributed. He will be a finalist, competing with either Phelps or Murray.

At this point, I must introduce readers to a new psephological concept. It is “Condorcet winner” called after the French mathematician, philosopher, historian and republican politician, Marie Jean Antoine Nicolas de Caritat, Marquis de Condorcet (1743-94). It is defined as “a candidate in an election who can defeat any other candidate in a pair-wise contest.” The classic recent case of a Condorcet winner is Scott Morrison. The classic recent case of a Condorcet loser is Julie Bishop.

What killed Bishop’s chance to become Prime Minister was the existence of a “Stop Dutton at Any Cost” campaign. The line of argument was that if Morrison was second to Dutton on the first count, he would win because all of Bishop’s votes would transfer to Morrison. However, if Bishop was second to Dutton, then too many Morrison votes would transfer to Dutton. So Bishop was a guaranteed Condorcet loser. Her position was, more or less, the same as Murray’s in the by-election.

The problem for those who would say “Stop Sharma at Any Cost” is that a mass electorate of 110,000 voters in Wentworth cannot be relied upon to behave like an elite electorate of 85 federal politicians of the Liberal Party. Consequently, whereas Rebekha Sharkie was always likely to be a Condorcet winner in Mayo against Georgina Downer, Phelps is not likely to be a Condorcet winner against Sharma.

In a nutshell, the natural Labor vote in Wentworth is quite high. Consequently, Phelps is likely to come third with enough of her preferences “leaking” to Sharma – and giving him victory. Consequent upon the Labor vote being naturally quite high, Labor cannot be expected to “run dead”, as happened in Mayo.

The media tells us that “Wentworth is Australia’s Wealthiest Electorate”. In two senses that is true. Wentworth has more voters who are “seriously rich” than any other. It also has the highest incomes, well ahead of the second highest, which is North Sydney. However, it also has a substantial number of high-income earners who rent and live in modest dwellings. Labor does very well among renters who live in modest dwellings!

For that reason, Wentworth is not “blue ribbon Liberal” to my way of thinking. It used to be (in the fifties) when its boundaries were roughly the same as are those of the present state seat of Vaucluse. That state seat is a genuine “Blue ribbon Liberal” electoral district. The federal seat of Wentworth is not.

For that reason, my concept of wealth is different. My concept is “relative socio-economic advantage rank” and it goes in this order: Bradfield, Berowra, North Sydney, Mitchell, Warringah, Ryan, Curtin, Kooyong, Mackellar, Goldstein and Wentworth. The next down is Canberra in which I live. It is a safe Labor seat!

Suppose Turnbull had been the member for Bradfield, Berowra, Mackellar or North Sydney, then Labor would have “run dead”, as they did in Mayo. The essential reason why Sharma is more likely to win than not is that the Labor vote is too high. Labor cannot “run dead” in Wentworth because it has some chance of winning. It would have no chance in Bradfield, Berowra, Mackellar or North Sydney. Therefore, Phelps is likely to come third. The candidate who comes third is a guaranteed Condorcet loser.

Malcolm Mackerras is Honorary Fellow of Australian Catholic University. malcolm.mackerras@acu.edu.au