Election forecasting

Voice Referendum #1 – My Forecast Explained

October 13, 2023 By Nigel Marriott

Australians will reject the proposed constitutional amendment known as The Voice in a referendum on 14^th October 2023. My forecast is for NO to win the national vote by 17 percentage points and win the state count 6-0.

This article was first published on 11th October 2023. My forecast then was for NO to win 16 points and the state count 6-0.

UK General Elections #5 – How accurate are voting intention polls? – updated with GE19

December 29, 2019 By Nigel Marriott

After 3 general elections with severe polling errors, the UK opinion pollsters redeemed themselves in the 2019 UK General Election with their most accurate performance since 1955. I base this statement on data provided by Mark Pack who has systematically recorded every opinion poll published since 1945. The challenge now for the industry is to maintain this level of performance for the next election which may be easier said than done given that 5 out of the last 8 elections have experienced a major polling error.

UK General Election 2019 #2 – My forecast is the most accurate & beats the Exit Poll!

December 16, 2019 By Nigel Marriott

At 2200 on Thursday 12th December 2019, the BBC/ITV/Sky Exit Poll was revealed to the nation and pointed to a large majority for the Conservatives. Unlike 2017, I was able to turn to my wife and say “it looks like I will be right this time!” By the end of the night, Gavin Freeguard from the Institute of Government was tweeting that not only was I the most accurate election forecaster of 2019, I was more accurate than the Exit Poll.

UK General Election 2019 #1 – My Official Forecast

December 12, 2019 By Nigel Marriott

My forecast for the 2019 UK General Election this Thursday is that the Conservatives will win a majority of 72 seats. The margin of error in this forecast is very wide though due to the fact that 5 of of the last 7 general elections have seen a major polling error. If there is a repeat of the GE2017 underestimate of Labour, then there will be another hung Parliament.

EU Election 2019 #1 – How many MEPs will each party win?

May 21, 2019 By Nigel Marriott

Here is my forecast for the election that was not supposed to be happening in the UK. The Brexit Party is well on course to be the largest party and could even set the record for the best ever vote share by a party in the d’Hondt era of EU elections in the UK. At the same time, the Liberal Democrats have the possibility of beating both the Conservatives and Labour parties in a UK-wide election for the first time since 1906.

US Presidential Election 2020 #1 – Will Donald Trump win a 2nd term in 2020?

October 30, 2018 By Nigel Marriott

In a week’s time, Americans will go to the polls for what is known as the mid-term elections. Inevitably, the results will lead to much speculation on what it means for Donald Trump’s chances of re-election in 2020. However, I will be surprised if many commentators will look to history as a guide to 2020 and so I will fill in this gap with the help of fun 10 question quiz about US presidents.

Forecasting#2 – Do Election Pollsters Show Forecasting Skill?

September 28, 2018 By Nigel Marriott

As I write this, a plethora of economic forecasts are making the rounds in the news in the UK. In all cases, the forecasters have failed to publish their track record and these days, I will not pay attention to what they say unless their forecasts are accompanied by a track record. But, how does one go about presenting a forecasting track record to prove that one has forecasting skill? To demonstrate, I will analyse how well opinion polls have predicted General Elections in the UK and measure their track record. I must confess I was surprised at what I found out and I would urge all opinion pollsters to take note of my results.

UK General Election 2017 #7 – Review of my predictions

July 9, 2017 By Nigel Marriott

Exactly one month ago, the UK woke up to the news they had elected a hung parliament for the second time in three elections. For many forecasters including myself, this came as a surprise as I had been predicting a Conservative majority of 100 seats. In the event, the largest ever polling underestimate of the Labour vote was enough to see the Conservatives lose their majority.

At the beginning of my commentary on election night itself, I defined success for my forecasts as being how close the number of Conservative seats was to my forecast of 375. I also stated that if the number of seats was in the 340s I would consider this to be a prediction error. The final outcome was 317 seats so clearly that is a major prediction error.

**Update 20th Sept 2025 – This post was originally published 9th July 2017. It remains one of my most important posts but it did contain some graphics which were unreadable in some formats and some typos so I’ve edited this post to correct these issues. I’ve also updated the text format to my current style guide and taken the opportunity to add links to subsequent posts which reinforce particular points made in this article. Any new links are pointed out**

UK General Elections #2 – How accurate are the opinion polls? – updated with GE17

July 2, 2017 By Nigel Marriott

Ahead of the 2017 general election, I predicted that the opinion polls would be wrong again and that the Conservatives lead over Labour would be underestimated by 2.6%. I based this on data provided by Mark Pack who has systematically recorded every opinion poll published since 1945. In the event, I was right that the polls would be wrong but instead of an error favouring the Conservatives, the polls recorded the largest ever underestimate of the Labour vote. As a result, election forecasters were blindsided yet again and the result was a hung parliament which few saw coming.

UK General Election 2017 Results #1 – My Election Night Commentary

June 9, 2017 By Nigel Marriott

Friday 07:35 – I’ve just woken up to the result that we have a hung parliament which is miles away from my prediction. Clearly I need to conduct a post-mortem of my model but I did state in my first chart of this post (see bottom of post) that a hung parliament would occur if the CON-LAB lead was under 3%. Sure enough that is the outcome with the BBC currently saying the CON-LAB lead is 2.3%. What it also means that we have another epic polling error as the average of all polls in the week before the election showed a CON-LAB lead of 7.5%. Unlike 2015 when all pollsters got it, congratulations must go to Survation who called it spot on.

I am sure we will have a wave of people claiming to have predicted this error. As far as I am concerned a valid prediction is only one made in public in advance. Such a prediction would also need to explain why they expected a polling error on the scale shown in the chart.

The last time such an error occurred was 1983 and the error is on the scale of 1951! In fact the error is even more remarkable if you look at the 3 main parties.

Another polling post mortem beckons but this election will go down in history.