Thursday 29 January 2015

ELECTION FORECASTS NOWCAST, IF THE #GE2015 WAS HELD TODAY

The votes and seats totals shown elsewhere on this site are forecasts.  They are predictions about what will happen on 7 May 2015.  These forecasts are based on where we think the polls are today, combined with historical evidence about how support for parties evolves as elections approach.  As such, they will have significant uncertainty until just before the election.  Because they are predictions about what will happen on 7 May, there is no way to evaluate them until the election occurs.
This tab provides our estimates of what constituency polls conducted today in every constituency would find.  This is not exactly an estimate of what would happen in an election today, and it may not exactly match the current national polls.  Since Lord Ashcroft Polls is currently publishing the vast majority of constituency polls, these Nowcasts specifically aim to predict where those polls would find each constituency in the question “Thinking specifically about your own Parliamentary constituency at the next General Election and the candidates who are likely to stand for election to Westminster there, which party's candidate do you think you will vote for in your own constituency?” 
This Nowcast allows us to evaluate the performance of our model at interpolating the likely situation in unpolled constituencies every time Lord Ashcroft releases polls of previously unpolled constituencies.  While there are many other aspects of our forecasting model, one important component is to correctly determine what is likely to be happening right now in unpolled constituencies, or in constuencies that have not been polled in many months, and so the degree to which we are successful at that is important.  Every time there are new constituency polls released, we will write a blog post evaluating how well our Nowcasts predicted those constituency polls at the LSE General Election blog.
Here are our estimates of what these hypothetical constituency polls would look like in every GB seat:
Sortable table of current vote share for every party in every seat.
Sortable table of current probability of victory for every party in every seat.
If we aggregate the vote shares to the regional level, we get these totals:
  Con Lab LD SNP PC GRN UKIP Oth
East Midlands 32 35 7 0 0 6 19 1
East of England 37 22 11 0 0 8 22 1
London 29 43 10 0 0 7 10 1
North East 20 49 7 0 0 6 18 1
North West 24 45 9 0 0 5 16 1
Scotland 12 31 7 43 0 4 2 1
South East 41 19 12 0 0 7 18 2
South West 36 19 17 0 0 9 18 1
Wales 19 40 8 0 12 4 16 1
West Midlands 31 35 7 0 0 6 20 2
Yorkshire and The Humber 23 41 8 0 0 6 20 1
If these seat predictions and vote predictions were aggregated up to the GB level, we get these totals:
Party Lo Seats Hi Swing Lo Votes Hi Swing
Conservatives 248 254 262 -52 29.4% 29.8% 30.2% -7.1%
Labour 294 302 311 44 31.8% 32.3% 32.7% 2.6%
Liberal Democrats 19 22 25 -35 9.5% 9.8% 10.1% -13.7%
SNP 35 41 46 35 3.5% 3.6% 3.8% 1.9%
Plaid Cymru 1 2 3 -1 0.5% 0.6% 0.6% -0.0%
Greens 1 2 3 1 6.2% 6.5% 6.8% 5.6%
UKIP 5 8 10 8 15.8% 16.1% 16.5% 13.0%
Other 1 1 1 0 1.2% 1.3% 1.4% -2.3%

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