Forecast update: 5 December 2014

Forecast b 141205

Labour are back in front in our forecast. The Conservatives have dropped a point in our polling average, putting them on 31% to Labour’s 33%. That two-point lead, five months from Election Day, is enough to give Labour a 53% chance of being the largest party, up from 47% last week.

It’s just the fifth time since last October that we’ve made Labour favourites to win most seats. (Note that we’ve never had them as favourites to win the most votes.)

There are a couple of important caveats to bear in mind. First, almost all of the polling in our average took place before the Autumn Statement. (The exception, from YouGov, shows no sign of a Conservative bounce yet.) Second, as the election draws nearer, our probabilities are increasingly sensitive to slight movements in the polling average. We should therefore be cautious about reading too much into a change in the probabilities – even one of 10 percentage points – unless it is sustained over a few weeks.

Two trends are clear, though: since we launched our model, the chances of a Hung Parliament have risen from 40% to 58%.

Hung Parliament trend 141205

Also, the combined share of the vote for the Conservatives and Labour in our central forecast has fallen from 69.3% to 64.5%. For those two plus the Liberal Democrats, it’s down from 85.0% to 75.3%.

Three party trend 141205


Date of forecast: 5 December 2014
Days till the election: 153

Inputted current average poll shares
Con: 31%
Lab: 33%
LD: 8%
Others (inc. UKIP): 28%
– UKIP: 16%

Forecast Election Day Shares (with 95% Prediction Intervals)
Con: 33.6% (±6.7, i.e. 27% – 40%)
Lab: 31.0% (±5.0, i.e. 26% – 36%)
LD: 10.8% (±6.6, i.e. 4% – 17%)
Implied point estimate shares for:
– Others (inc. UKIP): 24.6%
– UKIP: 14.1%

Forecast Election Day Seats (with approximate 95% Prediction Intervals)
Con: 292 (221 – 373)
Lab: 298 (221 – 365)
LD: 29 (24 – 35)
(Prediction intervals assume LD & others shares at central forecast, Con & Lab shares vary as per prediction intervals)

Central forecast: Lab largest party, but short of a majority by 28

Approximate probabilities of key outcomes
Con largest: 47%
… with a majority: 18%
Lab largest: 53%
… with a majority: 23%
Hung Parliament: 58%
… with Con largest: 28%
… with Lab largest: 30%
(probabilities may not sum due to rounding)

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