Forecast update: 5 May 2015

Forecast main 150505

Two days to go, and it’s a tossup.

Our model now gives David Cameron and Ed Miliband each a 50% chance of being Prime Minister after the election. Neither has much hope of a majority: we give the Tories a 9% chance of winning 323+ seats, and Labour less than a 0.1% chance. That means a 91% chance of another hung parliament.

The main movement in our polling average since Friday is a 1-point gain for the Liberal Democrats, to 9%. The Tories retain a 1-point lead over Labour, 34% to 33%, while UKIP are still on 13%.

Our central forecast has the Tories and Lib Dems each doing about 1 point better than the current polling average, and Labour and UKIP each doing about 1 point worse.

In that scenario, the Tories win 35% of the vote and 289 seats, 34 seats short of a majority but ahead of Labour on 32% and 257. The Lib Dems get 26 seats with 10% of the vote and UKIP get 3 with 12%. Meanwhile, the SNP win all bar 6 of Scotland’s 59 seats.

That central forecast would mean the Conservatives could just form a majority with the Lib Dems and the DUP (for a total of 324 seats).

Because of their willingness to work with either Labour or the Conservatives, we give the Liberal Democrats a 53% chance of being part of the majority grouping – slightly higher than either of the two larger parties – even if we assume they won’t join one involving the SNP.


Date of forecast: 5 May 2015
Days till the election: 2

Inputted current average poll shares
Con: 34%
Lab: 33%
LD: 9%
UKIP: 13%
Others: 11%

Forecast GB Vote Shares (with 95% Prediction Intervals)
Con: 35% (31% – 39%)
Lab: 32% (28% – 36%)
LD: 10% (7% – 14%)
UKIP: 12% (9% – 16%)
Others: 11% (9% – 12%)

Forecast Scotland Vote Shares (with 95% Prediction Intervals)
SNP: 48% (44% – 52%)
Labour: 27% (23% – 31%)

Forecast GB Seats (with 95% Prediction Intervals)
Con: 289 (248 – 331)
Lab: 257 (216 – 295)
LD: 26 (17 – 35)
SNP: 53 (45 – 57)
PC: 3 (2 – 3)
UKIP: 3 (3 – 4)
Grn: 1
Other: 1
(May not sum to 632 due to rounding of sums of probabilities.)

Central forecast: Con short of a majority by 34
(Criterion for majority now changed to 323 not 326, assuming Sinn Fein win 5 seats and do not take them.)

Probabilities of key outcomes
Con most votes: 78%
Lab most votes: 22%

Con most seats: 74%
Lab most seats: 26%

Hung Parliament: 91%
… with Con largest: 66%
… with Lab largest: 26%

Probabilities of predicted government outcomes:
(See here for explanations and assumptions)

Con majority: 9%
Con+DUP: 7%
Con+LD: 20%
Con+LD+DUP: 15%
Con largest, Lab+SNP+DUP+other left maj: 6%
Con largest, but Lab+SNP+other left maj: 14%
Con largest, but Lab+SNP maj: 4%
Lab largest, Lab+SNP maj: 7%
Lab+LD+DUP+SDLP+PC+Grn+Hermon: 7%
Lab+LD+DUP: 5%
Lab+LD: 5%
Lab+DUP: 0%
Lab majority: 0%

(Probabilities may not sum due to rounding)

Shares trend

Shares trend b

2 thoughts on “Forecast update: 5 May 2015”

  1. I am troubled by your definitions – GB includes Scotland but the SNP is not shown as getting a % of the GB votes? Are you saying it does not?
    Because this election is (a) very much a matter of very fine voting margins & (b) almost definitely will give a hung Parliament, it behoves you to get into the small party detail. Include the DUP, Greens etc etc. Shae on you for not – dumb!

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