Forecasting model

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.

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 2017 General Election Forecast #3 – A Description of my Final Model

May 30, 2017 By Nigel Marriott

For the last 6 weeks, I have been making forecasts of the number of seats that each party will get in the 2017 General Election. If you have been following my forecasts, you will know that I have developed a variety of prediction models which all predict something different. With 10 days to go, I decided it was high time to settle on a single Final Model which is described in this post.

Forecasting#1 – How do you identify a good forecaster?

April 3, 2017 By Nigel Marriott

“I think the people in this country have had enough of experts”

Michael Gove, Sky News, 3^rd June 2016

This was one of the most memorable quotes during the EU referendum in 2016 and came in response to a question as to why the forecasts of a whole list of organisations such as the IMF should be ignored. It prompted a flurry of rebuttals and articles supporting or damning him and the debate has not gone away.

Like so many quotes, it has already become distorted. I strongly recommend you listen to the full question and answer because here is his quote in its entirety.

“I think the people in this country have had enough of experts… from organisations with acronyms saying that they know what is best and getting it consistently wrong.”

When I read this full quote I realised I am in complete agreement with Michael Gove.

By-Elections #2 – Review of Copeland & Stoke Central predictions

February 24, 2017 By Nigel Marriott

The results are in and it is now time to review my predictions of the Copeland and Stoke-on-Trent Central by-elections. How well did my by-election model do and what lessons can be learnt? Let’s look at the numbers first.

By-Elections #1 – How to predict outcomes in the Brexit era

February 19, 2017 By Nigel Marriott

Since the UK voted to leave the EU on 23^rd June 2016, there have been 3 contested parliamentary by-elections (Witney, Richmond Park, Sleaford & North Hykeham) and one uncontested by-election (Batley & Spen which was the late Jo Cox’s seat). Many commentators have analysed these results to see how the referendum result has impacted on parliamentary voting intentions. Whatever voter dynamics are revealed, it is reasonable to assume that they are likely to influence future by-elections. In late October 2016 just after the Witney result, I realised it could be possible to build a by-election model by combining two sources of data.

My own estimates of the Leave & Remain votes in each of the 650 parliamentary constituencies where I calculated that 400 out of 650 seats voted Leave.
My interpretation of the Lord Ashcroft “exit poll” carried out on 21^st to 23^rd June 2016 and published immediately after the results were announced.

At the time, I described my by-election modelling approach in a youtube clip and that is worth listening to. I have made some changes to my model since then so this post is the most up to date version of my model. I will illustrate the basic principle using the Witney by-election (David Cameron’s former seat) of 20^th October 2016 where the top line numbers are: