Latest voting intention and the impact of turnout

Here are the mid-week polls so far:

Kantar - CON 45%(+8), LAB 27%(nc), LDEM 16%(-1), BREX 2%(-7) YouGov/Times/Sky - CON 42%(-3), LAB 30%(+2), LDEM 15%(nc), BREX 4%(nc) ICM/Reuters - CON 42%(+3), LAB 32%(+1), LDEM 13%(-2), BREX 5%(-3) Survation/GMB - CON 42%, LAB 28%, LDEM 13%, BREX 5%

A few things to note. Kantar and ICM have now removed the Brexit party as an option in the seats where they are not standing, which will have contributed to the increase in Conservative support and decrease in Brexit party support (YouGov had already introduced this change last week).

The Survation poll is the first telephone poll that they've conducted in this election campaign (all their other recent polls have been conducted online), hence they've recommended against drawing direct comparisons with their previous poll. The fourteen point Tory lead in this poll is substantially larger than in Survation's previous poll, which had a lead of only six points, but it's impossible to tell whether that's down to an increase in Conservative support or the different methodology. At the last election their two approaches produced similar results, with their final poll being conducted by phone.

Finally, Kantar's polling has received some criticism on social media for their approach to turnout weighting, with "re-weighted" versions of their figures doing the rounds. The details of this criticism are wrong on almost every single measure. It's very easy for people to retweet figures claiming they show the turnout figures from Kantar, but it takes rather longer to explain why the sums are wrong Matt Singh did a thread on it here, and RSS Statistical Ambassador, Anthony Masters, has done a lengthier post on it here.

In short, the claims confuse normal demographic weights (the ones Kantar use to ensure the proportion of young and old people in the samples matches the figures the ONS publish for the British population as a whole) with their turnout model. Secondly, they compare youth turnout to early estimates straight after the 2017 election, when there have been subsequent measures from the British Election Study that were actually checked against the marked electoral register, so are almost certainly more accurate. Compared to those figures, Kantar's turnout levels look far more sensible. The figures do imply a small increase in turnout among older voters, a small drop amongst younger votes, but nowhere near the level that has been bandied about on social media.

However, if we leave aside the specific criticisms, it is true to say that turnout has different impacts on different pollsters. In the 2017 election many pollsters adopted elaborate turnout models based on demographic factors. These models largely backfired, so pollsters dropped them. Most polling companies are now using much simpler turnout models, that have much less of an impact, and which are based primarily on how likely respondents to the poll say they will vote.

Kantar is the exception - in 2017 they used a model that predicted people's likelihood to vote based on both how likely they said they were to vote, but also their past voting and how old they are. Unlike many other companies this worked well for them and they were one of the more accurate polling companies, so they kept it. That does mean that Kantar now have a turnout model that makes more difference than most.

Looking at the polls at the top of this post, factoring in turnout made no difference to the lead in YouGov's poll (it was a 12 point Tory lead before turnout weighting, a 12 point Tory lead afterwards). The same is true of Survation - their poll would have had a 14 point lead before turnout was factored in, and a 14 point lead afterwards.

In ICM's poll, without turnout the lead would have been 7 points, with turnout it grows to 10 points. With Kantar's latest poll, the tables suggest that the turnout weighting increased the Tory lead from 10 points to 18 points.

Hence, while the specific claims about Kantar are nonsense, it is true to say their turnout model has more impact than that of some other companies. That does not, of course, mean it is wrong (turnout is obviously a significant factor in elections). However, before going off on one about how important turnout weighting is to the current polls, it's rather important to note that for many companies it is contributing little or nothing to the size of the Tory lead.