How good was Yougov's election model?

Duncan Stott asked if anyone has done a proper bit of research into Yougov's projection. "No" is the answer, even after this effort.

As we would expect, strong confidence in the two biggest parties, slightly weaker for the LD. Something of a hefty miss for the SNP and for UKIP.

The Yougov model seemed to cap the LD vote at about 35% in any constituency. This puts an artificial ceiling on their performance, and costs a number of seats.

Overall, Yougov met or exceeded a hypothesis that "2015 predicts 2017 exactly".

Error watch

Yougov called the wrong winner in only 48 seats. What caused the errors? Primarily, not being held by Con or Lab; Yougov was wrong in 21/67 such cases.

Three seats went from "Con likely" to "Lab gain". Colne Valley, Warwick and Leamington, Portsmouth South. All were marked by a great increase in the Labour vote – from the LD in Portsmouth, from not voting in the other seats.

Mansfield went in the opposite direction, from "Lab likely" to "Con gain".

Lessons

From these initial investigations, we reckon Yougov worked well within the Butler model. They did well where the ConLab dominated discussion and votes. In a ConLab election, this was enough to look roughly right.

We're not convinced that they fully appreciated the swing from "No vote" to Labour. It is possible that this was corrected in later releases – we are working from the 2 June release, a week before the final score.

Yougov's performance in other areas was patchy, and we have no evidence on whether their model will work with three or more major parties.

Further research is needed.

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