Latest national poll median date: October 20
Projections reflect recent polling graciously made publicly available by pollsters and media organizations. I am not a pollster, and derive no income from this blog.

Thursday, August 29, 2019

Phone/IVR Polls vs. Online Polls

There has been chatter among some pollsters on Twitter (Frank Graves of EKOS and Quito Maggi of Mainstreet) that the NDP is in huge trouble - perhaps even in danger of being reduced to near zero. Lean Tossup did a blog post about this.

And yet, things don't necessarily look that critical in seat models: I have the NDP at 20.3 (18 projected ahead), 338Canada at 18.3 (16 ahead), the CBC Poll Tracker at 14 projected ahead, and Lean Tossup at 22 projected ahead.

Both EKOS and Mainstreet are IVR pollsters. So this got me thinking: what would my projection look like with only phone/IVR pollsters (who do probability sampling) vs. online pollsters (who can reach people that wouldn't pick up the phone, but have non-random samples)? (I tweeted a few days ago about pollsters' measurement of the crucial LIB-CON gap in ON.)

First, here are the full current toplines (little LIB tick from yesterday due to coming across decimal point data on a poll). Keep in mind that all figures reflect my turnout adjustment, which favours the Tories.

Projection as of the latest national poll (midpoint: August 21)
LIB - 153.8 (33.8%)
CON - 146.0 (36.3%)
NDP - 20.3 (12.9%), 18 ahead
BQ - 13.3 (4.3%)
GRN - 3.7 (9.5%)
IND - 0.5

PPC - 0.5
Effective sample size: 3,304 (single new poll unbiased relative to universe of pollsters)
If you're new to my 2019 projections, view key interpretive information here.

Explanation on effective sample size: my poll weighting method assumes that vote intentions evolve as random walks, and that each pollster is affected by a house effect (constant across all of that firm's polls) drawn from a normal distribution. The effective sample size is that of a poll with the same midpoint date as the latest poll (Aug. 21 here) with zero house effect that would have the same variance as the polling average.

(Note that in addition to the house effect, there is also potential error common to all pollsters. As that cannot be reduced through poll averaging, if it's taken into account, the effective sample size would drop drastically, to something around 370.)

Projection with Phone and IVR Polls only
LIB - 162.2 (34.7%)
CON - 144.3 (36.6%)
NDP - 13.4 (10.9%), 12 ahead
BQ - 12.7 (4.3%)
GRN - 4.5 (10.3%)
IND - 0.5

PPC - 0.5
Effective sample size: 1,240

Projection with Online Polls only
LIB - 150.1 (33.3%)
CON - 146.6 (36.1%)
NDP - 24.1 (13.7%), 21 ahead
BQ - 12.9 (4.3%)
GRN - 3.4 (9.4%)
IND - 0.5

PPC - 0.4
Effective sample size: 2,586

Keeping in mind that the margin of error is smaller around 11-14% than around 50%, and using the effective sample sizes, the difference between the NDP's 10.9% and 13.7% is statistically significant at the 5% level (and remains so if you cut the effective sample sizes by 1/3, since the surprisingly large NDP gap suggests I may have underestimated the variance of pollster house effects). It's hard to say if it's due to the phone/IVR vs. online issue or due to unrelated pollster house effects, but there appears to be a real difference between phone/IVR and online pollsters' measurement of the NDP.

- If you believe phone/IVR pollsters, the NDP is in grave danger of losing official party status: it would have been 50/50 for an election last week, and there are suggestions things have gotten worse.

- If you believe online pollsters, the NDP would have had a good chance of maintaining its seat count outside Vancouver Island and QC, and is very likely to have kept official party status.

The party most directly impacted by this is, unsurprisingly, the Liberals: they're either quite close to a majority (while losing the popular vote by 2%!) per phone/IVR, or basically even seat-wise with the Tories.

Regionally, this happens because, relative to the online projection, the phone/IVR projection has LIBs taking from CONs and the NDP in ON, and CONs taking from the NDP in BC. The effects pretty much cancel out for the Tories, who are in the mid-140s in both projections.

It will be interesting to see if this difference persists through the campaign. I will end by noting, perhaps ominously for the NDP, that in recent elections, when pollsters have disagreed about its prospects, the pollsters having it lower were almost always closer to the mark.

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