A record of forecasts vs. results can be found below - the barometer has only made the wrong call four times in 48 federal and provincial by-elections since 2012, for an accuracy rating of 91.7%.
Three of the four errors have occurred in Newfoundland and Labrador, where the Liberals have gone from a tiny share of the vote in 2011 to big by-election victories. In one of the ridings, there was a swing of almost 90 points between the Tories and the Liberals.
In the other 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%.
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.
A by-election has been called for the Manitoba riding of The Pas for April 21. By-elections have yet to be called for the federal ridings of Peterborough, Ottawa West-Nepean and Sudbury, and the provincial ridings of Jean-Talon in Quebec and Dartmouth South in Nova Scotia.
As the federal by-elections may never be called before the federal election scheduled for October, they are not tracked here.
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.
Despite being in the Quebec City region, where the Coalition Avenir Québec is stronger, Jean-Talon is a safe Liberal riding. Bolduc first won it in a 2008 by-election with 58% of the vote, and held on to it in the 2008 provincial election with 50%. His support dropped to 37% in 2012, but that improved back to 45% in 2014.
That Bolduc won the riding by some 10 points in 2012, when the Liberals were defeated, shows how safe the riding is for the PLQ. Perhaps more significantly, the party has held the riding since its creation in 1966.
So, the Parti Québécois and Coalition Avenir Québec can only vie for bragging rights. The edge would go to the PQ, which has placed second in every election since 1970. Even with the ADQ made its breakthrough in 2007, the PQ placed in second place by a comfortable margin. But in 2014, the PQ took 22%, just up on the CAQ's 21%, so there is the potential for more of a race.
If the recent poll by CROP showing a sharp decline in Liberal support turns out to be the start of a trend, and not an outlier, Jean-Talon could be a bit closer than expected. Another wild card, though, is the PQ's leadership race. Polls have suggested that Pierre-Karl Péladeau will boost the PQ if he wins, and a recent poll gave the party enough of a boost with Péladeau as leader to make Jean-Talon a riding that could potentially swing. But more realistically, it should stick with the PLQ.
Forecast history: Was STRONG LIBERAL at Bolduc's resignation.
The riding has a rather kaleidoscope history, having been held by the Liberals, New Democrats, and Tories at some point during the 1990s.
As Dartmouth South-Portland Valley, however, the riding swung towards the New Democrats in dramatic fashion. The party increased its share from 43% in 2003 to 48% in 2006 and finally 55% in 2009. The Liberals placed third in 2009 with 29%.
But in the last election, the riding swung heavily towards the Liberals, as occurred province wide. From a 28-point NDP victory (on the transposed boundaries), the Liberals won it by 13 points with 46% to 33% for the NDP. The Tories were third with 18%.
With the Liberals still leading very comfortably in the polls and the New Democrats having fallen further back, Dartmouth South should remain in Liberal hands.
Forecast history: STRONG LIBERAL since Rowe's passing.