With the federal election campaign officially starting this weekend, Stephen Harper's Conservatives and Tom Mulcair's New Democrats are neck and neck in national voting intentions, with Justin Trudeau's Liberals falling increasingly behind.

The latest update from the CBC Poll Tracker puts the NDP narrowly ahead at 32.1 per cent support, followed closely by the Conservatives at 31.6 per cent. The Liberals, at 25.6 per cent, come up in third.​

The Greens and Bloc Québécois round out the list with just under five per cent apiece.

If an election were held today, this would likely deliver 113 to 151 seats for the Conservatives, 114 to 140 seats for the New Democrats, and 62 to 94 seats for the Liberals. The Bloc would likely win up to two seats, while Elizabeth May of the Greens would likely be re-elected to the House of Commons.

There is a lot of overlap between the Conservative and NDP tallies, but the Tories do hold a slight advantage and would most likely end up with a plurality of seats. The NDP and Liberals, however, would easily win a majority of seats between them.

Polling trends clear

Polls released over the last week have shown clear trends in how voting intentions are shifting. Polls by Forum Research (for the Toronto Star), EKOS Research (for iPolitics), and Ipsos Reid (for Global News) have all shown a similarly positive trend for the Conservatives, and negative movement for the Liberals, since they were all last in the field together at the same time at the end of June. Since then, the Conservatives have picked up between three to five points in each of these three polls, while the Liberals have dropped between three and four points. The New Democrats appear to be wobbling back and forth within the margin of error.

Indeed, since the Poll Tracker update of June 29, the New Democrats have not moved at all. The Conservatives, however, have picked up 3.2 points while the Liberals have dropped 1.7 points. This represents significant movement in an aggregation of all publicly available polls.

But the future is unknown

Though the numbers point to a close race between the Conservatives and New Democrats, campaigns matter — particularly when they are twice as long as the norm.

The 2011 campaign is proof of that. Four polls were conducted in the final days before the writs were dropped on March 26 of that year. Altogether, they averaged 39 per cent support for the Conservatives, 25 per cent for the Liberals, and 17 per cent for the NDP. In Quebec, the Bloc Québécois was dominant with 39 per cent support.

On election day, the Conservatives took 40 per cent of the vote, with the NDP capturing 31 per cent, the Liberals 19 per cent, and the Bloc just 23 per cent in Quebec. The NDP's tally in that province went from 16 per cent in the polls, before the election officially began, to 43 per cent at the ballot box.

That is not to say that the polls were wrong about the state of the race when it kicked off in 2011, but rather that opinions can change over the course of a campaign. And that campaign was just 37 days long. Now, with 11 weeks to go before casting a ballot, Canadians have much more time to change their minds — even again and again.

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.

The questions asked in the polls mentioned in this article were as follows:

Forum: "If a federal election were held today, which party are you most likely to vote for?"

EKOS: "If a federal election were held tomorrow, which party would you vote for?"

Ipsos Reid: The question asked was not included in Ipsos's release.