In our last article we introduced the TGIAF General Election 2015 simulator, an interactive version of which is available here.
Today we will look at the results from 1000 simulations of our model, an approach we took with our World Cup simulator. By doing so many simulations, the results will be very close to the "true" probabilities within our model, and we can therefore make reasonably confident predictions.
As there are no other candidates with odds given in the Buckingham constituency, John Bercow has been given a 100% chance of success in our model.
The good news for the party is that they have a 82.2% chance of at least maintaining their current position of one MP, and a 46.3% chance of improving upon it. However, as the party has been occasionally polling ahead of the Liberal Democrats in opinion surveys, it is an indictment of the UK's voting system that the Greens will see such a low number of MPs. On the crowd-funded Vote for Policies website, visitors have to pick their preferred policies, without knowing which party they come from. On this site, the Green party have a clear lead over all six major national parties, so their low profile nationally could be considered a success story for a media industry which doesn't want to encourage progressive politics.
Plaid currently have three seats, and the model predicts that this is the party’s most likely result from the upcoming election, at 36.3%. Perhaps as an indicator of how Plaid’s standing has largely remained the same since 2010, they have an almost equal chance of losing seats (32.5%) as gaining (31.2%).
Scottish National Party
The extent to which the SNP are expected to thrive next year is shown by the fact that every simulation shows the party improving on their current 5 seats, with a 82.8% probability of having MPs numbering in the 20s.
United Kingdom Independence Party
After UKIP polled the highest of any UK party in the 2014 European elections, it is perhaps to be anticipated that they will follow it up with large gains in the general election, with a 53.8% chance of at least 30 MPs, and a 99.0% chance of at least 20. This very strong performance within the model is due to UKIP being the party which is represented in the joint-most constituencies, 500, the same as the Conservatives, with Labour being represented in 492 (a reminder: in each constituency only parties with odds under 100/1 are considered).
Liberal Democrat Party
With all this in mind, the party will probably see a victory over UKIP in the battle for third place as a major victory, and this is what the model leans towards, with 71.9% of simulations ending with the Lib Dems having more seats (and 5.0% ending with a tie between the two parties). This may be seen as a bit of a shock, with UKIP consistently polling higher than the Lib Dems (YouGov have had UKIP poll higher than the Lib Dems in every poll since April 2013). However, we earlier mentioned that UKIP are represented in a large amount of constituencies, it could be that their supporter base is spread a lot thinner than other parties. The Lib Dems are also benefitting from their current seats, where disapproval with individual MPs is less than disapproval with the party as a whole. If this is the case, than it may be somewhat of an irony that the referendum decision to reject the Lib Dem’s proposal for an alternative vote system may preserve their position as the third-biggest party in the UK.
With the party currently holding 303 seats, the distribution above clearly shows that the party will see some kind of loss in the spring, with a 28.3% chance of that loss being at least 50 seats.
However, despite these struggles, our model predicts Labour to see an increase on their current tally of 254 MPs, with 74.7% of simulations seeing Labour make a gain of at least 30 seats. It is clear that Labour are roughly predicted to finish with more seats than the Conservatives within our model, but of course, the two results aren’t independent. Therefore, we need to look at the combined results for these two parties.
Conservatives versus Labour
- Conservative win: 5.0%
- Labour win: 93.7%
- Tie: 1.3%
This is a surprisingly strong prediction from the model, and will be good news for Ed Miliband and his party. The extent of Labour’s advantage is apparent on the second picture on the slideshow, which shows the Conservative lead over Labour. Here we can see that Labour’s lead could be reasonably significant. Indeed, 53.0% of simulations saw a Labour lead of at least 20 seats.
However, aside from Labour’s advantage, the other striking aspect of our results is the lack of any majority. With 650 seats available, 326 are needed for a majority. The closest any party was to a majority was Labour, with 300 in one simulation, and this isn’t anywhere near. Therefore, perhaps the strongest prediction our model makes is that no party will be in complete control of the country in spring. Given the disaster for the Liberal Democrats that entering a coalition was, it seems likely that no party will be eager to be a junior partner in a coalition, so we might be seeing the first minority government since 1997.
Prediction ranges and expected seats
For each party we will give the 95%, 75% and 50% prediction ranges. These are just the ranges within which that percentage of results fell into. If a party’s 95% prediction range is from 90-110, then this means that we have 95% confidence in such a result.
We will also give the expected number of seats for each party. This is simply worked out by summing the party’s probabilities across every constituency they stand in. So for example, if a party stood for four seats, and had chances of winning those of 75%, 50%, 15% and 4%, then their expected number of seats would be 0.75 + 0.5 + 0.15 + 0.04 = 1.44.
Below are these statistics for each party, along with their minimum and maximum seat return (which essentially make up the 100% prediction range):
As 95% is the standard confidence level used in formal statistics, we will treat any outcome with a likelihood of more than 95% as a fully confident prediction. So, to summarise the results, our predictions for the 2015 general election are as follows:
- There is a 93.7% chance of a Labour victory
- The Lib Dems have a 71.9% chance of holding on to third place, ahead of UKIP
- UKIP will gain at least 20 seats, whilst the SNP will gain at least 10
- No party will hold an overall majority, leading to another hung parliament
It will be exciting for us here to see if the results in the spring fall within our 95% prediction ranges.