By Stephen Fisher, John Kenny and Rosalind Shorrocks.

This is our first post since the Manchester bombing. We would like to take this opportunity to extend our sympathy to all those affected, directly and indirectly. Now that the political parties are campaigning again we hope that it is not insensitive of us to update our forecasts.

In truth, because of Monday’s terrible events it is not clear how our forecast should be interpreted. Only one poll conducted since the attacks has been published, so most of the changes in the opinion poll data, and the models that are built on them, reflect polls conducted late last week; shortly after the Conservative manifesto launch and mostly before Theresa May’s announcement of a cap on social care funding. Those polls showed a considerable tightening of the Conservative lead and so a reduction in the predicted Tory majority.

Overall, our combined forecast of the Conservative majority has dropped to 100, down from 123 last week and from 132 two weeks ago.

The combined probability of a Conservative majority, at 87% has correspondingly taken a small dip from 91% last week. More strikingly the probability of a Conservative landslide (a 100+ seat majority) has fallen from 64% (and 71% two weeks ago) to just 34% this week. The citizen forecast component of this average has not changed due to lack of new data. Previously that component was pulling down the average. Now it is pushing up. The markets and our pseudo-probability from the polls are both around 30%. Intriguing there is some inconsistency between the PredictIt market suggesting a 27% probability of a 100+ majority and the spread-betting markets pointing to a 110 seat majority.

Continue reading Combined forecast for GE2017: second update →

By Stephen Fisher, John Kenny and Rosalind Shorrocks.

Since our first forecast combining different indicators of the election outcome last week, the Conservatives and particularly Labour have edged up in the polls at the expense of UKIP and the Liberal Democrats. The crucial Conservative-Labour lead in the polls this week has varied from between 13 to 20 points. On average the lead has narrowed by just under two points to 16.5.

In line with this movement in the polls, the predicted Conservative majority from the betting markets and the simple models has dropped, but not, intriguingly, in the complex model forecasts. On average, our combined forecast is for a Tory majority of 123; down a little from 132 last week but still a big win.

The combined probability of a Conservative majority, at 91%, has remained unchanged from last week. However, the probability of a Conservative landslide has taken a small dip to a 64% chance (down from 71%). This drop is almost entirely due to Labour’s better performance in more recent polls, resulting in fewer leads for the Conservatives of 16 points or more required for a 100+ majority (the basis of our pseudo-probability from the polls).

Continue reading Combined forecast for GE2017: first update →

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 8^th 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.

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.

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.

Methodology

Continue reading First Combined Forecast for the 2017 general election →