A record of forecasts vs. results can be found below - the barometer has only made the wrong call once in 30 federal and provincial by-elections since 2012, for an accuracy rating of 97%.
Note that the one error, in the Newfoundland and Labrador riding of Virginia Waters, was won by a handful of votes by the Liberals, who were given a 33% chance of taking the riding by the model. The PCs were awarded a 61% chance of winning, two points above the bar for being considered a 'Toss-Up'.
What the By-Election Barometer is
The By-Election Barometer tracks all scheduled and upcoming federal and provincial by-elections. The percentages shown in the charts represent margins, colour-coded according to the standards adopted by this site. The first set show the results of the last two elections.
The second set of margins are those that the projection model churns out when each regional/provincial poll is applied, using the same system as ThreeHundredEight's standard seat projection model. These are a way to demonstrate what might be expected in the riding, based on regional trends. The rolling 30-day average calculates an unweighted average of the last 30-days of regional polling.
The third set of margins, when available, represent the results of actual polls of the riding that have been released.
Finally, ThreeHundredEight's Forecast is calculated by taking the projected range of results from the average of the last 30 days of polling, including any polls done for the riding itself, and comparing how the ranges for each party overlap. The amount of overlap that potentially puts a party in a position to win is then tallied, the result being a percentage "chance" of that party winning the riding.
A Strong result means a 95% to 100% chance of winning, Likely is a 75% to 94% chance, Lean is a 60% to 74% chance, and Toss-Up means the chances of a party winning are 59% or less.
The Wildcard section describes any factor that could make the result unpredictable.
What it isn't
The By-Election Barometer is not a poll, the section titled "Margin after application of swing from regional polls" is not a list of riding polls, and the 30-day average is not a projection. By-Elections are notoriously hard to call, and the Barometer is not a tracking of actual voting intentions. The forecast is also not an opinion. As always, I am tied to what the numbers show.
By-elections have yet to be called in the federal ridings of Macleod and Fort McMurray-Athabasca in Alberta and Trinity-Spadina and Scarborough-Agincourt in Ontario, and in the provincial riding of Brampton-Springdale in Ontario.
Weighted averages and support ranges
When available, polls for by-elections have been weighted using the same aggregation methodology employed elsewhere on the site. The confidence intervals are based on the standard deviation from the mean of past errors in by-election polling. What this means is that based on how by-election polls have been wrong in the past, we can expect the results to fall within the 68% confidence interval (one standard deviation) 68% of the time, and within the 95% confidence interval (two standard deviations) 95% of the time.
This is in contrast to the margins of error normally reported in by-election polls: often +/- 4%, 19 times out of 20. While this may be the correct margin of error to apply to a true random sample, recent experience has shown that this confidence interval has not been reliable. Instead, to have confidence that the results will be accurate 19 times out of 20, we need a margin of error of about +/- 8%. The confidence intervals calculated below reflect this.
It is hard to find a safer riding for the Conservatives than Macleod. Menzies won it with 77% of the vote in both the 2008 and 2011 elections, after taking it with 75% in 2004 and 2006. Between the 1988 and 2000 elections, the combined tally of the Reform/Canadian Alliance and Progressive Conservatives in the riding ranged between 81% and 84%. The best the Liberals have done since then was just 16% in 1993, while the NDP has not done better than the 10% it took in 2011 over that time.
Macleod is as secure as it gets. The only battle in this riding will be for the Conservative nomination. Who places second may be an interesting footnote, but that is about it.
Forecast history: Has been, and will remain, STRONG CONSERVATIVE from Menzies' resignation.
The Conservative Party and its predecessors have held the riding since the 1950s. In 2011, Jean took 72% of the vote to just 13% for the NDP and 11% for the Liberals. The last time the riding was not won by a majority of the vote was in 1993, when the Reform candidate captured 47% of it.
So it is unlikely that either the Liberals or the New Democrats will be able to make a major run at the riding. But after the results in Provencher and Brandon-Souris last year, we should not under-estimate the ability of the Liberals to make some serious inroads.
In fact, recent polling in Alberta has been not bad for the Liberals, though the latest surveys show a return to normalcy and, accordingly, is now considered a STRONG CONSERVATIVE. But the margin of victory secured in the last few elections may be halved.
Forecast history: Was STRONG CONSERVATIVE at Jean's resignation. LIKELY CONSERVATIVE on February 21. Returned to STRONG CONSERVATIVE on April 11.
She first won the seat for the NDP in 2006, taking it away from Liberal incumbent Tony Ianno. At the time, the riding had been Liberal since the 1993 election, when it was won from the NDP. If we stretch the riding's history into the old Spadina riding, it was held by the NDP for most of the 1980s, before which it was Liberal going back to 1962.
It makes Trinity-Spadina a sort of anti-Conservative bellwether riding. Going back to the (first) Trudeau years, the riding elected Liberals when that party formed government, and elected New Democrats when the PCs or Conservatives came to power. In other words, it is the kind of riding that the Liberals win when they are doing well and lose to the NDP when they are not.
That would seem to bode well for the Liberals, who are leading in the polls in Ontario. The New Democrats have taken a step backwards compared to their showing in 2011, which should automatically make Trinity-Spadina a riding that could swing back over to the Liberals. But Chow won the riding by more than 30 points in the last election with 55% support. As the Liberals were at only 23%, that makes it a long hill to climb for the party.
But 2011 was a bit of an anomalous year. The riding had only been won by either Ianno or Chow by less than 10 points in every election from 1997 to 2008. It seems likely that Trinity-Spadina will revert to that pattern. However, the by-election in Toronto Centre suggested that the NDP can hold its own in a competitive Toronto race and do better than the province-wide polls suggest they should.
Put it all together, and it makes Trinity-Spadina a riding that is likely to be held by the NDP.
Forecast history: Was LIKELY NEW DEMOCRAT at Chow's resignation. Became STRONG NEW DEMOCRAT on April 11.
Many recent by-elections, and upcoming by-elections, have been in very safe Conservative seats. This one in Scarborough-Agincourt will be in a very safe Liberal seat - really, virtually all of the 34 ridings retained by the Liberals in the 2011 cull are bare-bones Liberal ridings. But in the last five decades, Scarborough-Agincourt hasn't been represented by a Liberal for a grand total of six years. The last non-Liberal in Scarborough-Agincourt was a member of Brian Mulroney's government.
Karygiannis won the riding handily for many years after 1993, with margins of 30 to 40 points. That shrank to 27 points in 2008 and again to 11 points in 2011. But with the Liberals up in the polls in Ontario, there is very little chance that the Conservatives, down in the polls, will be able to wrestle this riding away from Justin Trudeau. As in those Alberta ridings for the Tories, the real contest may be for the Liberal nomination.
The by-election will serve as a decent test of Liberal strength in secure ridings, however. Will the party put up a number like in 2008 or 2011, when the party was drifting nationally, or will they put up a result like in the days of Liberal governments under Jean Chrétien and Paul Martin?
Forecast history: Was a STRONG LIBERAL at Karygiannis's resignation.
The riding, and its two predecessors, swung over from the Progressive Conservatives to the Liberals in 2003, when Dalton McGuinty was first elected premier. Apart from a big win by Jeffrey in 2007 by almost 20 points, Brampton-Springdale has not been the most secure of Liberal seats in the GTA. With the polls showing a tight race between the OLP and the PCs province wide, that would likely be the case again in a new vote.
In 2011, the Liberals took the riding with 44% to 36% for the Tories, while the NDP was well behind at 15%. With the loss of their incumbent and the polls not improving since 2011, the Liberals are at risk of losing the seat. But they do have the inside track.
Forecast history: Was LIKELY LIBERAL at Jeffrey's resignation. Became LEAN LIBERAL on April 11.