A record of forecasts vs. results can be found below - the barometer has only made the wrong call three times in 43 federal and provincial by-elections since 2012, for an accuracy rating of 93%.
The first error, in the Newfoundland and Labrador riding of Virginia Waters, was in a by-election won by just 40 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'.
For the second error, the Progressive Conservatives won the Alberta riding of Calgary West by 2.8 points over Wildrose, who were favoured. In the model, Wildrose was given a 65% chance of winning, with the Tories at 35%.
In the third error, again in Newfoundland and Labrador (Conception Bay South), the election was decided by 76 votes.
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 these projections with 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 are scheduled for November 25 in the provincial ridings of Trinity-Bay de Verde and Humber East in Newfoundland and Labrador. By-elections have yet to be called for the federal riding of Peterborough and the provincial ridings of Lloydminster in Saskatchewan, The Pas in Manitoba, Richelieu in Quebec, and Sudbury in Ontario.
This riding has tended to go with the governing party, being held by the PCs from 2003, the Liberals from 1989, and the PCs before that. It may be ahead of the curve if it goes with a Liberal MHA in this by-election, as it is expected to.
Trinity-Bay de Verde has been won by comfortable PC margins since 2003, with Johnson taking 63% in that election, 72% in 2007, and 62% in 2011. Over that time, the Liberals have taken between 23% and 32% of the vote. Considering the gains the party is making in the polls, that is enough of a base to wrest the riding away from the government, as we have seen elsewhere.
Forecast history: Was STRONG LIBERAL from Johnson's resignation.
Humber East has been one of the safest ridings for the Tories under Marshall. He first won it with 60% of the vote in 2003, but increased that to 84% in 2007. His share fell slightly to 78% in 2011, but that was still a huge margin.
The Liberals, who held the riding from 1996 to 2003, were previously the main opponents. The party took 40% in 2003. But that plummeted to 11% in 2007 and then just 8% in 2011. The NDP moved into second with 13% in that election.
But the New Democrats have taken a big step backwards. The Liberals have shown an uncanny ability to win by-elections in Newfoundland and Labrador, even from very low bases of support. While the model points to a LIKELY PC victory for now, I would not wager against the Liberals.
Forecast history: Was STRONG PC from Marshall's resignation, became LIKELY PC on October 31.
The riding is a safe one for the governing Saskatchewan Party, which has held it since 1999. McMillan first won it in 2007 with 61% of the vote, and he increased his share to 66% in 2011. The New Democrats captured just 29% of the vote in that election, making Lloydminster almost representative of the province's wider opinion.
That being the case, Lloydminster is a lock for the popular Saskatchewan Party. It will be interesting, though, to see if the NDP can make some gains or if the Liberals or Greens can make a splash in a low-stakes by-election.
Forecast history: Was STRONG SASK. PARTY from McMillan's resignation.
The Pas is a very solid and very safe NDP riding in Manitoba. It has been held by the party since 1969, and since 2003 has been won with at least 65% of the vote. Whitehead captured it with 73% in 2011, little different from the 75% he took in a 2009 by-election.
The Progressive Conservatives took just 23% of the vote in 2011, with the Liberals at an infinitesimal 3%.
Despite the NDP's sharp drop in the polls, that margin is still too wide for the Tories to overcome. By-elections can be strange beasts, of course, and perhaps the Tories' momentum combined with a strong showing by the Liberals, who have put up good numbers in recent by-elections, could make it close. But the riding is considered a STRONG NEW DEMOCRAT.
Forecast history: Was STRONG NEW DEMOCRAT from Whitehead's resignation.
Though Zakaïb's vote share dropped between 2012 and 2014, from 43% to 39%, her margin actually increased by a little more than a point and 600 votes. And Richelieu has been safely in the PQ camp since 1994.
After tanking, the PQ's support in the polls has reset somewhat. Nevertheless, it leaves the riding vulnerable to a flip. The CAQ is doing well enough in the polls, and though its support fell from 32% to 27% here over the last two elections, it remains in the best position to capture the riding from the PQ. The Liberals, who took 26% of the vote, could also make some noise in a close three-way race, but the polls do not suggest the party is poised to make gains. It leaves Richelieu to be a likely CAQ/PQ contest, and a test of the PQ's ability to remain the alternative to the Liberals in rural francophone Quebec.
Forecast history: Was TOSS-UP (CAQ/PQ) from Zakaïb's resignation, became TOSS-UP (PQ/CAQ) on October 31. Became STRONG PARTI QUEBECOIS on November 21.
There is some speculation that the by-election will never be held, with the date for the vote instead being set to coincide with the next federal election.
Peterborough is the kind of riding that could swing to the Liberals in the next election. Del Mastro won there three times, increasing his vote share from 36% in 2006 to 47% in 2008 and finally to 50% in 2011.
It used to be a safe Liberal seat, however, being won between 1993 and 2004 with between 44% and 48% of the vote each time. The Liberals fell to third in 2011 with 21% (the NDP moved into second with 25%) but with their strong polling numbers in Ontario are poised to potentially win it back.
Unlike other ridings in the wider GTA, Peterborough is one of those on the bubble, rather than one that should swing strongly to the Liberals. If a by-election is held, it could be a close one.
Forecast history: Was TOSS-UP (CPC/LPC) at Del Mastro's resignation, became TOSS-UP (LPC/CPC) on November 14.
After being a safe seat for the Liberals, over the last few years Sudbury has been a close race. Rick Bartolucci routinely won the riding by comfortable margins after his first victory in 1995, topping out at 69% of the vote in 2003. That fell to 59% in 2007, 42% in 2011, and then 39% when Andrew Oliver tried and failed to hold the seat for the Liberals.
Cimino won it instead with 42%, little different from the 41% the party took in its losing bid in 2011. So the riding is likely to be another close NDP/OLP battle.
The PCs should not be much of a factor, having captured just 14% in each of the last two elections (and just 8% in 2007). The party did hold the riding in the 1980s. In fact, Sudbury has been a swing riding for most of its history, having voted PC, Liberal, and NDP on multiple occasions (even CCF in the 1940s).
The polling that has been done since the last general vote has been generally favourable to the Liberals, in that they have mostly kept their place while the NDP has slipped back. That should make Sudbury liable to a flip, but the race has been so close over the last two elections that it stands to be the case again when the by-election is called. It also stands to be dominated by local factors, as is often the case in northern Ontario.
The Liberals have a bit of an edge because their candidate would sit on the governing benches if elected, but much could depend on the quality of the candidates named by both parties.
Forecast history: Was TOSS-UP (NDP/OLP) at Cimino's resignation.