Category Archives: Methodology

Local elections, Methodology

Calculating the Local Elections Projected National Share (PNS) and Projected House of Commons in 2021

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By John Curtice and Stephen Fisher.

This post is a revised and updated version of a similar post from 2019 here.

A key summary statistic of the outcome of each year’s annual round of local elections is the so-called Projected National Share (PNS). This is an estimate of the share of the vote that the principal parties would have won in a GB-wide general election if voters across the country as a whole had behaved in the same way as those who actually voted in the local elections. It provides a single, seemingly straightforward measure of party performance that can tell us not only how well or badly a party has done as compared with four years ago (when, typically, most of the seats up for grabs were last contested), but also as compared with any previous local election for which a PNS is available – even though the places in which local elections are held varies considerably from one year to the next.

In this blog we provide some guidance as to how the PNS is being calculated this year by the BBC and how it will be used to project an outcome in terms of House of Commons seats.

Continue reading Calculating the Local Elections Projected National Share (PNS) and Projected House of Commons in 2021 →
EU referendum, Methodology

How the BBC will be benchmarking the results on EU referendum night

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by John Curtice and Stephen Fisher.

Referendum night is going to represent something of a departure from usual. There will not be the drama of an exit poll announcement to stir excitement – and possibly shock – at 10pm. Meanwhile, when the actual results do start to be announced, except in Northern Ireland they will not be declared by the parliamentary constituencies with which we have all become familiar. Rather they will be unveiled local authority by local authority. As a result, we will get just one declaration for the whole of Birmingham, while, at the other end of the spectrum, the Isles of Scilly will get their moment in the sun.

But perhaps the biggest departure from the routine of election night will be that there will be no ‘last time’ against which to compare the results as they are declared. So when Sunderland or Swindon announce their result we will not be able to say whether it represents a ‘swing’ to Remain or Leave – and thus for which side, if either, it represents a good result.

To overcome this problem we have, on behalf of the BBC, been beavering away at establishing which local authorities appear to be more likely to record a relatively strong vote for Remain, which are the ones where Leave can be expected to do relatively well, and which are the council areas where the two sides could be expected to be equally matched. Our evidence has come primarily from a dataset of over 61,000 interviews about people’s attitudes towards the EU. These interviews were conducted with people in Great Britain by YouGov between March of last year and March of this year and we are deeply grateful to the company for making these data available.

Continue reading How the BBC will be benchmarking the results on EU referendum night →

Combined forecast, EU referendum, Methodology

A combined forecast for the UK’s EU membership referendum

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Stephen Fisher and Rosalind Shorrocks

There is a lot of evidence from the academic research on forecasting that suggests it is a good idea to combine information from different sources (e.g. here). In US and German elections generating a forecast by combining the forecasts of others has a good track record. For the upcoming US presidential election pollyvote.org provides an average of different forecasts together with excellent summaries and discussions of the different methods and forecasts.

We have developed a similar method of combining forecasts for the UK’s referendum on EU membership on 23rd June 2016. The summaries of the average forecast win-probability and share of the vote for Remain by method and then overall are presented in the tables below. Note that there are different components for each because some of the source forecasts provide only probabilities or only vote share.

Share of the vote Remain Leave
Combined forecast (mean) 53.6 46.4
Betting markets 53.9 46.1
Polls 51.4 48.6
Expert forecasts 56.0 44.0
Volunteer forecasts 54.6 45.5
Poll based models 54.0 46.0
Non-poll based models 52.0 48.0
Probability that Remain wins
Combined forecast (mean) 66.8
Citizen forecasts 64.3
Volunteer forecasts 71.2
Prediction markets 65.4
Betting markets 62.2
Polls 63.0
Poll based models 74.7

Continue reading A combined forecast for the UK’s EU membership referendum →

Local elections, Methodology

Forecasting Local Election Seats 2016

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by Stephen Fisher

Local elections are supposed to be about local matters, but the electoral fortunes of councillors and would-be councillors depend very heavily on the popularity of their parties nationally. So the outcome of this year’s local elections depend on how the current standing of the parties compares with four years ago when the seats up for election this year were last contested.

In the run up to the 2012 local elections Labour were polling above 40% with a solid 9 point lead over the Conservatives, in part because of the so-called omnishambles budget. Meanwhile the Liberal Democrats had slumped in the polls after the formation of the coalition government with little over 11%.

According to the average of the most recent polls from six companies, Labour have dropped since 2012 to 35% now, only narrowly ahead of the Conservatives who are on 34%. The Liberal Democrats have slid even further to just 7%. On this basis alone we should expect both Labour and the Lib Dems to lose substantial numbers of council seats while the Conservatives should make gains from their 3-point recovery. Continue reading Forecasting Local Election Seats 2016 →

EU referendum, Forecast updates, Historical & polls based forecast, Methodology

First Forecast for the Brexit Referendum

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By Stephen Fisher and Alan Renwick

The UK will have a referendum on whether to remain in or leave the EU on 23rd June 2016. We have developed a method for forecasting the outcome based on current vote intention polls and analysis of opinion polls from previous referendums from the UK and across the world. Continue reading First Forecast for the Brexit Referendum →

General elections, Israeli Elections, Methodology

Salutary lessons from the Israeli election polls 2015

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by Stephen Fisher

Publishing polls in the last five days before an election is illegal in Israel, so the final pre-election polls were published on 13th March. They suggested that Binyamin Netanyahu’s Likud party would get around 22 seats to 25 for the Zionist Union (the alliance between Labor and Haunuah, led by Issac Herzog and Tzipi Livni).

The exit polls yesterday suggested 27 each.

The actual result was 30 for Likud and 24 for the Zionist Union. Continue reading Salutary lessons from the Israeli election polls 2015 →

Methodology, US elections

A guide to the US midterm election forecasts

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Stephen Fisher and Jonathan Jones

Tomorrow Americans go to the polls for the midterm elections. All 435 seats in the House of Representatives are up for election, as well as 36 Senate seats and a host of state and local offices.

The historic tendency for the President’s party to lose ground in midterm elections, is sufficiently strong to say that there is virtually no chance of the Democrats regaining control of the House. Meanwhile the experience of previous midterm elections with a second-term President suggests that the Republicans should have a decent of winning the extra six seats they need to take control of the Senate.

Not only history but also political and economic circumstances in recent months, and especially current polls for individual Senate races suggest the Republicans have, according to the main forecasters, at least a two-thirds chance of achieving a Senate majority.

We are not attempting to forecast the outcomes of any of these elections, but several others with excellent track records for US election forecasting are. This article purely provides some introduction and links to the forecasts and offers some commentary from a British election forecasting perspective. We consider the House forecasts before turning to those for the Senate. Continue reading A guide to the US midterm election forecasts →