No one believes Queensland's Nationals leader Lawrence Springborg will be that state's premier after next Saturday's election. Peter Beattie's Labor government holds 66 of the parliament's 89 seats, and the swing required to oust him is 10per cent.

But as a recent exchange on the Crikey website between Democrats number-cruncher John Cherry and ABC election analyst Antony Green illustrated, those figures belie a closer contest.

To understand why, let's brush up on Australia's voting system by looking at the French one. There, votes are cast for a field of candidates. If no one receives more than 50per cent support, voters return two weeks later to choose from the two frontrunners.

In Australia, we do something similar but all on the same day by ranking candidates. A politician's primary vote is like the French first-round support, and the two-candidate-preferred vote (after preferences) roughly equates to the French second round.

But this is complicated by our compulsory versus optional preferential voting (CPV and OPV).

By law, Australians must go to a polling booth, but we don't have to register a vote.

However, under CPV (used at federal elections), if we do vote, we "must number every square". This is like telling the French that voting is optional but if they do it in round one, they must do it again in a fortnight.

Queensland uses OPV, so you can number as many squares as you wish - like being able to attend either or both French rounds.

For the purposes of this exercise, imagine French law saying that if you vote for a candidate in round one, and that candidate survives to round two, you must vote for them again.

We can now look at next Saturday's vote as a two-round contest.

At the last Queensland election, in 2001, 10per cent voted in the first round but not the second. They had no influence on the outcome. And about three quarters of that 10per cent were conservative supporters.

This happened because the conservative vote splintered from the coalition to One Nation and others, and because people just voted "one", their votes went nowhere when their candidate dropped out of the count.

The conservative vote is expected to substantially return to the coalition next Saturday. In addition, Liberals and Nationals have agreed not to run in the same seats, and the Greens are contesting more electorates, so siphoning ALP votes. Fewer Queenslanders, therefore, will abstain from round two, and more of those who do will be Labor supporters.

Cherry sees the coalition winning five seats from the government - without taking one vote from it. Green writes that if Queensland used CPV, Beattie's majority would shrink by eight, and Springborg's required swing would only be 6.8per cent.

You can quibble with their numbers, but what they say is almost certainly true: tens of thousands of anti-Labor Queenslanders - who wasted their votes in 2001 - won't be wasting their vote again next Saturday.

Peter Brent is editor of mumble.com.au.