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UK election summary

The Conservative party, led by Theresa May, defeated the Labour party, led by Jeremy Corbyn.

The Conservative party got 42% of the vote, Labour got 40% of the vote, and all the other parties received 18% between them. The Conservatives ended up with 51.5% of the two-party vote, just a bit less than Hillary Clinton’s share last November.

In the previous U.K. general election, two years ago, Conservative beat Labour, 37%-30%, that’s 55% of the two-party vote.

The time before, the Conservatives received 36%, compared to Labour’s 29%. The Conservatives again had received 55% of the two-party vote.

As with the Clinton-Trump presidential election and the “Brexit” election in the U.K. last year, the estimates from the polls turned out to give pretty good forecasts.

The predictions were not perfect—the 318-262 split in parliament was not quite the 302-269 that was predicted, and the estimated 42-38 vote split didn’t quite predict the 43.5-41.0 split that actually happened (those latter figures, for Great Britain only, come from the Yougov post-election summary). And the accuracy of the seat forecast has to be attributed in part to luck, given the wide predictive uncertainty bounds (based on pre-election polls, the Conservatives were forecast to win between 269 and 334 seats). The predictions were done using Mister P and Stan.

The Brexit and Clinton-Trump poll forecasts looked bad at the time because they got the outcome wrong, but as forecasts of public opinion they were solid, only off by a percentage point or two in each case. In general we’d expect polls to do better in two-party races or, more generally, in elections with two clear options, because then there are fewer reasons for prospective voters to change their opinions. In most parts of the U.K., this 2017 election was a two-party affair, hence it should be no surprise that the final polls were accurate (after suitable adjustment for nonresponse), even if, again, there was some luck that they were as close as shown in these graphs by Jack Blumenau:

P.S. I like Yougov and some of our research is supported by Yougov, but I’m kinda baffled cos when I googled I found this page by Anthony Wells, which estimates 42% for the Conservatives, 35% for Labour, and a prediction of “an increased Conservative majority in the Commons,” which seems to contradict their page that I linked to above, with that prediction of a hung parliament. That’s the forecast I take seriously because it used MRP, but then it makes me wonder why their “Final call” was different. Once you have a model and a series of polls, why throw all that away when making your final call?

9 Comments

  1. dsquared says:

    Answer to your PS question is one part

    “cowardice and herding”,

    and one part

    “the MRP model was brand new and highly dependent on the baseline assumptions (Lord Ashcroft’s MRP model delivered disastrous results because it was calibrated to 2015 rather than a new panel), so I can kind of see how they didn’t want to stake the whole company’s credibility on an outlier prediction from it, although ex post don’t they wish they had”.

    • Andrew says:

      Dsquared:

      That could be, but then I’d prefer Yougov to be more clear on all this when presenting their results.

      – In the pre-election post where they gave that “final call,” they could’ve added something like, “We also have a model-based estimate developed by political science and using statistical adjustments, which predicts the Conservatives to win between 269 and 334 seats, with a best estimate of 302 seats and a hung parliament.”

      – And, in the post after the election, they could’ve added something like, “But the above forecast is not the only thing Yougov reported. Actually, our ‘final call’—which did not make use of our full skills of statistical adjustment—predicted the Conservatives would have an increased majority.”

      From a media-relations point of view, though, sure, maybe they played it just right by having two forecasts that didn’t refer to each other.

  2. jrkrideau says:

    The Conservative party, led by Theresa May, defeated the Labour party, led by Jeremy Corbyn.

    I don’t think you quite appreciate how a multi-party, British-style, parliamentary system works in a case like this. Theresa May lost big time even if she may be able to remain in power with a DUP deal.

    Corbyn did not “win” the election but in practical terms he did well. He has defeated his nay-saying Labour/Blairite enemies and looks like a real alternative to the Conservatives in the next election.

  3. Jeremy Fox says:

    Re: your ps, YouGov polled the race using two different methods: https://yougov.co.uk/news/2017/06/07/two-methods-one-commitment-yougovs-polling-and-mod/. FiveThirtyEight included results from both methods in their tally of the UK polls: https://fivethirtyeight.com/features/uk-election-hung-parliament/

  4. jrkrideau says:

    Given the problems we have seen with other polls I am impressed with the YouGov results. Except for the SNP losses they were pretty close (as in horseshoes?) and even Nicola Sturgeon thought they would take some loses though perhaps not this many.

  5. Matt Kosko says:

    “The predictions were not perfect—the 302-269 split in parliament was not quite the 310-257 that was predicted”

    I think the split is 318-262, isn’t it?

  6. A.G.McDowell says:

    Statistically, 302-269 may be pretty close to 318-262, but the political consequences are quite different. A majority is in theory 325 (in practice less because Sinn Fein don’t take up their seats) and the DUP have done a deal for support which adds 10 seats. The Ulster Unionists have a track record of doing deals to prop up minority governments, and they hate Corbyn because Corbyn has links to the IRA and other organisations dating back to when they were killing people. At 302 seats I think the price would be coalition government, if it was feasible to create a working government at all.

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