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Liberal leader Justin Trudeau speaks about his private member’s bill during a news conference Wednesday June 11, 2014 in Ottawa. THE CANADIAN PRESS/Adrian WyldAdrian Wyld/The Canadian Press

The next federal election is scheduled to take place just less than 16 months from today. There is even speculation that the vote could come earlier, putting us within 12 months of the next election. As it stands, Justin Trudeau's Liberals hold a comfortable lead over the governing Conservatives in the polls. But does that tell us anything about what the election result will be in 2015?

Polling conducted one year out from an election has a mixed record. In the federal and provincial elections held in the last six years – 17 in all – in a majority of cases the party holding the lead in polls conducted 12 to 16 months before the vote won on Election Day. But it is a slim majority, as this occurred just 10 times out of 17 cases. In other words, the chances of a party winning the next election when leading in the polls a year out are only a little better than a coin toss.

In fact, the party leading in the polls has had a harder time than other parties. On average, its support has dropped by 0.5 points between their average performance in the polls a year out and their election result. By comparison, the party running second in the polls has seen its support grow by an average of three points, while the party running third in the polls has had an average growth of 1.8 points.

Those are all relatively modest shifts, and ones that the Trudeau Liberals would happily take. In total, it would entail a reduction of the lead they currently hold over the Conservatives by 3.5 points. But since the beginning of 2014, the Liberals have averaged a lead of 5.9 points over the Tories.

But the average performance of the polls 12 months out from an election masks the wide swings that have taken place in individual cases. The B.C. Liberals, for instance, were polling almost 19 points below their eventual vote share one year before the 2013 provincial election. The Progressive Conservatives in Newfoundland and Labrador were polling about 20 points above where they ended up a year later in the 2011 provincial election.

There were double-digit shifts between the polls one year out and the election result for the Quebec Liberals in 2014, the Alberta Liberals and Coalition Avenir Québec in 2012, the PEI PCs and Newfoundland and Labrador NDP in 2011, the New Brunswick Tories and NDP in 2010, and the Quebec Liberals and ADQ in 2008.

On average, the polls have had a margin of error of +/- 6.3 points for each of three main parties one year before the election was held. The way Canadians vote in the 2015 federal election, then, could be very different from the way they say they would vote today. Twelve months before the 2011 election, the Conservatives held a four-point lead over the Liberals, with the NDP at just 17 per cent. On election night, the Conservatives would increase their support by seven points, the Liberals would be down 10 points, and the New Democrats up almost 14.

But that does not necessarily mean that the polls today bear no relation to where the parties will find themselves next year. There are several cases of support changing very little in the year before an election.

The most noteworthy recent example might be the 2008 federal election, when Stephen Harper's Conservatives were re-elected with a minority government. Polls conducted a year before that vote showed a much closer race, but nevertheless pointed to another Conservative minority. NDP support differed by just over a point, while both the Tories and Liberals were pegged to within four points a year before the vote.

In the 1984, 1993, 1997, 2000, and 2004 federal elections, the party leading in the polls a year earlier did indeed prevail. Over the last 30 years, only in 1988 and 2006 did the party leading in the polls 12 months before the election go to defeat. That might seem like good news for the Liberals, but in both cases it was the Liberal Party that lost.

Another bad omen for the Liberals is that in four out of the seven cases in which the party trailing in the polls a year out was eventually victorious, it was the incumbent government that came from behind to win (the Liberals in Quebec in 2008, Ontario in 2011, and B.C. in 2013, as well as the NDP in Manitoba in 2011).

However, in only one of the seven recent cases where the party trailing in the polls a year before the election made a comeback (the upset in British Columbia) did the party trail by a larger margin than the federal Conservatives currently do. The Liberals hold the advantage in the polls today, and that suggests the odds are narrowly in their favour for 2015. But it is far from a safe bet.

Éric Grenier writes about politics and polls at ThreeHundredEight.com.

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