Are the Conservatives mounting a comeback thanks to the Universal Child Care Benefit, or is the latest poll to get tongues wagging in Ottawa an outlier, soon to be forgotten?

The CBC Poll Tracker is now showing the Conservatives and New Democrats in a tie at 31.3 per cent each, with the Liberals trailing in third with 26.3 per cent.

While the Liberals are holding steady, the latest update represents a significant shift for the NDP and Conservatives. The New Democrats are down 1.1 points, and the Conservatives up 1.9 points, since the July 16 update.

That might seem marginal, but it is a massive swing in an aggregate that takes into account every poll.

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CBC Polls analyst Eric Grenier speaks with Abacus Data's David Coletto in the first episode of the Pollcast. (CBC)

Launching today is the CBC Pollcast, a podcast hosted by Éric Grenier that will delve deeply into the world of polling, their influence and the trends they are showing. There will be a new episode every week. This week's episode features Abacus Data CEO David Coletto, as he joins Éric to discuss how polls are conducted and the challenges facing the polling industry today.

Listen to the Pollcast below or download it here.

Welcome to The Pollcast, a podcast hosted by Éric Grenier that will delve deeply into the world of polling. This week's episode features Abacus Data CEO David Coletto. 19:04

And it is even more significant in the context of a close race. It has shifted the landscape from a likely NDP win to a likely Conservative plurality, with the Tories taking 113 to 150 seats and the NDP between 109 and 137 seats.

UCCB benefiting the Tories?

This Conservative surge in the aggregate is largely due to the Mainstreet Research poll published by Postmedia on Friday. It isn't the only sign of improving Conservative numbers, however, as Nanos Research's four-week rolling poll put the NDP and Conservatives in a tie at 31 per cent apiece earlier this week.

But the Mainstreet poll, with its 11-point Conservative lead and massive sample of more than 5,000 Canadians, has been the prime mover.

The poll is certainly widely out of step with other surveys. The last time the Conservatives registered a lead of this size was in a poll conducted more than three years ago. And a Forum Research poll, also released Friday but in the field a day before Mainstreet's, put the Conservatives behind by six points and in third place.

One important consideration is that Mainstreet is reporting the results of decided voters only, whereas many pollsters report the voting intentions of decided and "leaning" voters. If Mainstreet had gone with those numbers, the Conservatives would have a lead of six points with 35 per cent support, rather than 38 per cent. That would still represent a significant divergence from the polling consensus, but would have raised fewer eyebrows.

A major source of the discrepancy seems to be Mainstreet's result among Canadians between the ages of 18 and 34. Conservative support among Canadians 50 or older was well within the norm of what other surveys have recorded. But the poll awarded the Conservatives a big lead among the youngest cohort, with about 43 per cent support among decided voters.

Granted, the Canadians most likely to profit the most from the UCCB cheques sent out to their bank accounts and mailboxes on the very days that Mainstreet was in the field can be found in this age group, and those aged 35 to 49, who would also be getting many of these cheques, also reported higher Conservative support levels than other polls have suggested. But for the youngest group it still requires a swing of some 20 points in a matter of days.

The poll could prove to be an outlier (a naturally occurring phenomenon in random sampling) if future polls refute these results. Or, it could be the first survey to capture a powerful new trend towards the Conservatives. Time will tell.

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:

Mainstreet: "If the federal election were today, which party would you support?"

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

Nanos: "For those parties you would considering voting for federally, could you please rank your top two current local preferences?