With four weeks until election day, anyone seeking clarity in the polling numbers, or even a hint of where things could go from here, will be greatly disappointed.

The three-way race endures without an end in sight, and it appears that Canadians are little closer to making up their minds than they were when the campaign began.

The CBC Poll Tracker suggests the race to be at its closest yet, with only 0.9 percentage points separating the first-place Conservatives from the third-place Liberals. The Tories hold the lead, if it can be called that, with 30.5 per cent of the vote, against 29.8 per cent for the New Democrats and 29.6 per cent for the Liberals.

But while the polls have been solidifying around that 30 per cent mark for all three parties, people's opinions do not seem to be firming up.

The number of undecided voters can vary widely from poll to poll, depending on methodology and how these voters are defined. The latest numbers put the tally of undecideds at anywhere from seven per cent to 20 per cent. How these numbers have shifted since the campaign began, however, is more revealing: they haven't.

Polling averages as of Sept. 20. (CBC Poll Tracker)

Some recent polls show the number of undecideds actually higher at this stage of the campaign than earlier on. Some others show the proportion of undecideds falling slightly. None are recording a statistically significant change in the number of undecided voters, suggesting that this group is staying on the fence.

Will they vote?

That raises the question of whether today's undecided voters will even vote.

The assumptions many pollsters bake into their numbers are that undecideds will break proportionately to decided voters or that they won't vote at all, which essentially means they treat the totality of decided voters in their surveys as representative of the voting public.

But among those who say they have a preference, there are indications that they have not made up their minds either.

Polling by Ipsos Reid, asking Canadians whether they are "absolutely certain" they will vote for their party of choice, and Forum Research, asking respondents if they are "strong supporters" of that party, show little change since the first week of the campaign, even though you would expect voters to be firming up their convictions by now.

In early August, 54 per cent of Conservative voters told Ipsos they were absolutely certain they'd vote for that party. Last week, that had inched up to only 56 per cent. It is the same qualified response for the Liberals (40 per cent to 41 per cent) and the NDP (40 per cent in both cases).

Forum has shown slightly more movement (an increase of five points among those who say they are strong supporters of the Conservatives, a decrease of five for the Liberals), but nothing that cannot be chalked up to the margin of error.

What these numbers do suggest is that a lot of voters are still theoretically up for grabs. Maybe as many as half of NDP and Liberal supporters, and anywhere from two-fifths to one-fourth of Conservatives, are not completely committed to their respective parties.

Fewer Conservatives are willing to move, but on average the Liberals are almost twice as likely to be Tory voters' second choice than the New Democrats are. So if the Conservatives start to lose some of their uncommitted voters, it could benefit the Liberals.

There is little upside for the Tories, however, if supporters of the NDP or Liberals start to drift. The two parties are each other's second choice by a wide margin (and the Greens have more to gain from wavering New Democrats than do the Conservatives).

Of course, supporters of a given party are not homogeneous. The Conservative path to victory relies on peeling away the one-fifth of Liberal supporters who have the Conservatives as their second choice, without the NDP also picking up a large number of new votes from that direction.

For the New Democrats and Liberals, they primarily need to sway those NDP-Liberal swing voters over to their respective sides in order to win. That is less of a delicate balancing act than the Conservatives need to play, but as of yet it seems these left-of-centre swing voters are no closer to settling on one party. And nothing says they must before Oct. 19.

CBC's Poll Tracker aggregates all publicly released polls, weighing them by sample size, date and the polling firm's accuracy record. Upper and lower ranges are based on how polls have performed in other recent elections. The seat projection model makes individual projections for all ridings in the country, based on regional shifts in support since the 2011 election and taking into account other factors such as incumbency. The projections are subject to the margins of error of the opinion polls included in the model, as well as the unpredictable nature of politics at the riding level. The polls included in the model vary in size, date and method, and have not been individually verified by the CBC. You can read the full methodology here.