The most interesting poll appears only after a federal election. It is the Australian National University’s Australian Electoral Survey.

It asks: “When did you decide how you would definitely vote in this election?”

In 2004, 14.2% of respondents answered “A few days before the election”, with 8.6% saying they only made up their minds on the day. That means that at this stage in the last campaign, more than one in five voters had not yet made up their minds.

We are four days away from the election. All the polls point to a Labor win. But what if they are missing something? Labor only needs a swing of 4.8% to win government, but if things are like last time more than 20% of the electorate are yet to decide how they are going to vote.

Last week many papers ran photos of Kevin Rudd in his school nerd days, as captain of the Nambour High debating team. He seems to have forgotten one crucial lesson from back then. You can make a fantastic case in a debate, but if you do not rebut your opponents’ arguments you simply will not win.

There is a real danger in Rudd’s election strategy. He says he will barely change a thing. So why should voters change the government?

Crikey’s Morgan polling tries to identify “soft” Labor voters, people who believe the country is heading in the right direction, but still say they are voting Labor.

There are plenty of them. According to Morgan’s most recent face-to-face poll, 21% of all electors are soft Labor voters. What if they change their minds?

The polls say we will elect a Labor government, but they also say we believe the Liberals are superior economic managers, even after the recent interest rate rise. That contradicts political logic.

“I can’t explain why they are going to throw the government out,” one Labor MP told me last week. “I have a nagging worry they won’t.”

“They like the message, but they don’t like the messenger,” a senior Liberal staffer said of their research into voters’ views.

“They don’t like Howard, they don’t like Costello but they like the government and like Rudd,” another explained.

“Rudd’s popular, but he hasn’t made a case for change,” a minister claimed.

Liberal MPs say that they have not picked up any real anger with the government, yet report a desire for change. That is the conundrum of this campaign.

Kevin Rudd has said he is an economic conservative. For most of the time he has been Labor leader, he has gone out of his way to minimise the policy differences between his party and the Liberals. So if Rudd represents no change – or little change – why change governments? It would just be change for change’s sake.

Australians are conservative about changing federal governments. We have only done it five times since World War II, and never when the economy looks so robust.

Will the undecided voters back the government? Will the soft Labor voters stop their flirtation? The ANU’s Ian McAllister says undecided voters “tend to be swayed by policies, they tend to be swayed by their own particular economic self-interest”.

He describes them as “people who are making much more rational calculating decisions about their votes”.

Or will the votes of people yet to make up their minds likely to follow the direction the polls have pointed in all year? We will have the answer soon enough.