By Stephen Fisher, John Kenny and Rosalind Shorrocks.
The betting markets, polls, statistical forecasting models and volunteer forecasters are all pointing towards a landslide majority of around 132 for the Conservatives in the UK general election on 8th June. Surveys of citizen expectations are more limited and less clear, but by our analysis they suggest that 43% of people in society at large are expecting a Tory majority of over 100.
Historically the idea of combining forecasts from different sources has had a good track record, though it has to be admitted that our attempt to do one for the EU referendum did not work out well. Most recently the pollyvote.com combined forecast of the US presidential election last year was 2 points out on the share of the vote.
This is the first of our Combined Forecasts for next month’s general election in which we aggregate seats and vote share forecasts from a variety of sources including betting markets, polls, statistical forecasting models, volunteer forecast aggregators, and citizen forecasts. We will update weekly and the methodology (as detailed below) will evolve.
All the different sources point to a big Conservative win and there is little sign of doubt that the Conservatives will get at least a majority. Various different complex forecasting models are pointing to majorities for Theresa May of between 110 and 174, with an average of 130. Betting and prediction markets are just a little more bullish with an average majority of 146. Volunteers contributing forecasts to the Times Red Box sweepstake are only slightly more cautious. Details of the average estimate from each source, and the overall average number of seats expected for each party are in the table below. In addition to the big Conservative majority they collectively suggest that the Liberal Democrats seat tally will only increase by four and that the SNP will be down seven.
|Seats||Betting Markets||Complex models||Simple models||Volunteered||Average|
Not only are the headline forecasts from these sources remarkably strong for the Conservatives but the evidence from the polls and the models is consistent. There is also little sign of doubt among punters. The table below shows the implied probabilities of there being a Conservative majority and a Conservative landslide (100+ majority) from the betting markets, forecasting models (where available) and the polls (as judged by the proportions of polls showing the required lead). The citizen forecasts in the table show the proportion of respondents (excluding Don’t Knows) expecting each outcome. They are noticeably much more cautious and both ICM and YouGov surveys have shown as few as 30 per cent expecting a Conservative landslide.
|Probabilities||Betting markets||Statistical Models||Polls||Citizen forecasts||Average|
The sources for vote-share forecasts are more limited but again remarkably consistent across polls, markets and forecasting models. The polling average is an average of seven different polling averages. They are at best nowcasts rather than forecasts. The statistical models give actual forecasts. Even though the polls have underestimated the Conservatives and overestimated in the large majority of general elections, and substantially so in 2015, all but three of the four forecasting models with vote shares are expecting Labour to outperform the polls and the Tories to underperform. The betting markets are expecting the opposite; an even bigger Conservative lead than the polls are showing.
|% vote||Polling average||Betting markets||Forecast Models||Average|