Poll of polls: unpicking the latest forecasts

The Conservative share of votes stabilises as Labour slips to the benefit of the Liberal Democrats. Professor Leighton Vaughan Williams of Nottingham Business School's Political Forecasting Unit analyses the latest opinion polls.

There are two current national polls published today, from YouGov and Harris, and both show a ten point lead for the Conservatives over Labour.

This is an increase of a point for the Conservatives over the equivalent previous surveys, which arises not from any improvement in the Conservative share of the vote, but from a slight improvement in the Liberal Democrat showing at the expense of Labour.

Reproduced as a uniform swing across the country, the Conservatives would still be short of an overall majority, but the markets continue to bet on a clear Tory majority.

Polling Commentary
There are two current national polls out today.
YouGov/Sun: Con 40, Lab 30, Lib Dem 20
Harris/Daily Mail: Con 37, Lab 27, Lib Dem 22

In addition, there is another Harris poll for the Metro which shows the Conservatives on 37 per cent, Labour on 28 per cent and the Liberal Democrats on 20 per cent. But the fieldwork for this was conducted between 31 March and 6 April. In contrast, the fieldwork for the YouGov/Sun poll was conducted on the 8 and 9 April and for Harris/Daily Mail on the 7 and 8 April.

Essentially, we have a consistent picture emerging from the two latest polls, and this is of a stable Conservative share of the vote, with Labour support slipping a bit to the benefit of the Liberal Democrats. The broader picture is unchanged, however.

If the election was held today, the Conservatives would almost certainly win significantly more votes and more seats than Labour, though it is rather less certain that they would win enough seats to secure an overall majority.

Based on the two current national polls published today, and following the convention of rounding up, we have the following share of the vote.

Political Forecasting Unit's (PFU) "polling tracker" shows the same picture as the daily poll of polls. Put simply, the tracker is based on the most recent surveys by different polling organisations, and is adjusted so that the more recent the survey the more weight is attached to the vote shares. There is also some statistical smoothing which has the effect that outliers or vote shares that diverge most from the general consensus are allocated less weight.

Election barometer
The PFU's "election barometer", designed to capture the changing state of the race as it unfolds through the campaign, shows the polls predicting the Conservatives just falling short of an overall majority.
But an analysis of the money bet in political betting markets currently translates into a Conservative overall majority of 20, and a 61 per cent chance of a Tory overall majority.

Daily poll of polls
Conservative: 39 per cent
Labour: 29 per cent
Liberal Democrat: 21 per cent

PFU polling tracker (recent polls, weighted)
Conservative: 39 per cent
Labour: 29 per cent
Liberal Democrat: 21 per cent

Outcome (Based on polling tracker, assuming national swing reproduced in every constituency)
Conservatives: 319 seats
Labour: 247 seats
Liberal Democrat: 54 seats
Other: 30 seats
Conservatives short of an overall majority by seven

Where the money is (Analysis based on money wagered on the election in political betting markets)
Conservative: 335 seats
Labour: 221 seats
Liberal Democrat: 62 seats
Translates into a Conservative overall majority of 20

(Chances based on odds from betting exchanges)
% chance of Conservative overall majority: 61.2 per cent
% chance of No overall majority: 31.5 per cent
% chance of Labour overall majority: 7.1 per cent

Professor Leighton Vaughan Williams is Director of the Political Forecasting Unit at Nottingham Business School.

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