Doing the numbers in any political leadership race is a pointless exercise. For journalists it's futile, given those who admit to a favourite candidate, which are few and far between, are just as likely to switch their choices in another conversation depending on the track it's going down.

For the leadership contenders themselves it's even worse. If they take their soundings as being accurate they'd have to have close to 150 caucus members for the numbers to be true.

Many contenders have gone into their caucus room believing they've got it in the bag only to find out after the votes are cast that the bag's much lighter than they were led to believe.

It's called preservation. If a rookie MP, and there are 10 of them in the National caucus, is approached by one of the five leadership hopefuls, they'll simply tell them what they want to hear. They'll do that because telling someone vying for the top job that they're not up to it and that they'll be putting their vote elsewhere isn't career advancing, particularly if the hopeful goes on to win.

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That means there'll likely be more than one of the contenders going into the caucus next Tuesday believing they've got the numbers and will be genuinely surprised when it goes to a second ballot. The least popular will then drop off and votes from the dropout will transfer to other contenders, and that'll continue until that magic figure of 29, or 50 per cent plus one, is reached.

In theory the secret vote could go to several ballots but if it does the eventual winner will be about as popular as Andrew Little was when, with the help of the unions, he beat caucus favourite Grant Robertson by a hair's breadth.

At least with National MPs they have the say on who leads them without the cumbersome input of the card-carrying party membership. Jacinda Ardern avoided that process because it was so close to an election and that should serve as a lesson to Labour - leave the politics to the politicians.

Up for grabs next week will now also be National's deputy job, and that's a real contest considering the incumbent Paula Bennett wants to keep the job and is confident of doing so. Self preservation probably means she's had a positive vibe from her colleagues but there's angst in the party about the role she played during the last election, so her chance of survival is slim.

And the same goes for the new leadership aspirant Steven Joyce who, along with Bennett, is seen as the pill that Winston Peters found too bitter to swallow.