Now that I've hopefully finished making tweaks and refinements to the model, it's time to look at a number of "what would it take" scenarios. Below are some examples of national support levels that make the estimated expected seats (the numbers in the blog's right column) reach certain benchmarks.
Update Aug. 14: In light of today's news, I've added an alternative Conservative majority scenario primarily through a Liberal fall (rather than a Tory rise).
For each of these, I assume uniform national swing from the current projection: that is, changes in a party's support from current levels are the same in every region of the country. Two important caveats:
1. Regional support patterns can very well change during the campaign - we all remember Quebec swinging wildly the last two times - in which case these numbers can also change significantly.
2. The further down in the post you get, the larger the shifts involved, which means that those are even less reliable.
Therefore, please take everything with a grain of salt... and enjoy!
Tie for first place
CON 36.2% (148.3 seats)
LIB 32.4% (148.3)
NDP 14.0% (24.2)
BQ 4.1% (12.0)
GRN 10.0% (4.0)
The model suggests that if current patterns of regional support hold, the Tories need to win the popular vote by more than 3% just to get a tie.
LIB 35.1% (170.0)
CON 34.8% (131.5)
NDP 13.1% (21.5)
BQ 4.1% (9.9)
GRN 9.5% (4.1)
The model suggests that the Liberals can get a majority with not much more than 35% support and a tiny popular vote win. In fact, as I mentioned on Twitter a few days ago, a majority with a popular vote loss is possible.
Conservative majority (mainly through Tory rise)
CON 39.1% (170.0)
LIB 31.4% (132.5)
NDP 13.1% (19.9)
BQ 3.9% (10.8)
GRN 9.2% (3.8)
The silver lining for the Conservatives is that a majority is not out of reach. Indeed, if they return to their 2011 level (39.6%), they would likely get a majority, despite their inefficient vote this time.
Conservative majority (mainly through Liberal fall)
CON 37.3% (170.0)
LIB 27.7% (112.4)
NDP 16.1% (32.8)
BQ 4.4% (17.4)
GRN 11.4% (4.2)
If the Liberals weaken significantly, the Tories' majority threshold goes down, and the NDP gets to maintain its total of 28 seats outside Quebec (though with losses in Western Canada and gains in Eastern Canada). The Bloc also benefits.
NDP loses official party status
CON 36.7% (143.4)
LIB 35.4% (166.8)
NDP 8.7% (11.0)
BQ 4.4% (11.0)
GRN 11.7% (4.7)
The model thinks the NDP loses official party status when its support drops below roughly 9%. Fortunately for the NDP, even their worst polls still give them around 10% support, while their best ones give them in the mid-to-high teens. The NDP cratering would likely help the Liberals: notice how close they are to a majority in this scenario while losing the popular vote by over 1%.
Greens gain official party status
CON 33.1% (145.9)
LIB 29.5% (148.6)
NDP 10.7% (19.2)
GRN 19.5% (12.0)
BQ 3.4% (11.0)
The model is not well-suited to deal with this scenario, so take this with a big scoop of salt! In particular, with strategic voting and smart targeting, the Greens could reach 12 seats with a lot less than 19.5%. Presumably, if Green support reaches the mid-teens, we'll get lots of riding polls in districts that look the most promising to them - and incorporating those polls into the model would correct things.
That said, it can definitely happen for a third party's vote to be much more inefficient when it's on the way up (like the Green vote) than when it's well established (like the NDP vote) because voting habits adjust. For example, in the 1983 UK General Election, the Lib Dems surged, and it took them 25.4% (!) national support to get just 23 of 650 seats (which happens to be almost exactly the same proportion as 12 of 338). So it's not crazy to think that it could take the Greens 20% to get to the same place. Then, as the voters got used to the Lib Dems and could see where they're strong, they got twice as many seats (46 of 659) in the 1997 UK General Election on 2/3 of the vote share (16.8%) - somewhat similar to the NDP situation now.