Category Archives: Methodology

A guide to the US midterm election forecasts

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

After a year of forecasting, what’s changed?

Stephen Fisher, 24th October 2014

I first published a forecast of the 2015 general election result in October 2013. After taking on board comments and testing more candidate models, in February I revised the method from the one in this working paper to the one in this working paper. Both use opinion polls and election results going back to the 1950s to tell us what is likely to happen in this electoral cycle, and importantly, how sure we can be that it will happen. The historical pattern suggested governments tend to recover from mid-term blues while oppositions suffer a set back. Also the polls have tended to overestimate Labour and underestimate the Conservatives. Both factors suggested a Conservative lead at the next election. But also the variation in previous cycles was plenty enough to suggest very different outcomes were also possible if less likely.

Using a polling average for 8th October 2013 of Conservatives 32%, Labour 39% and Liberal Democrats 10% the revised method suggested a 42% chance of a Conservative overall majority. Over the last year the probability of a Conservative majority dropped steadily to 24% now. Why? Continue reading After a year of forecasting, what’s changed?

How accurate will the Scottish independence referendum polls be?

Stephen Fisher, 11th September

The vote intention polls for the Scottish independence referendum seem to have been taken largely at face value by commentators, politicians and even the financial markets. In particular, the roughly equal split of the vote between Yes and No in several recent polls is being interpreted as if it implies that the result of the referendum is likely to be close. But how accurate are opinion polls as predictors of referendum outcomes and how accurate are polls for elections in Scotland more generally? Continue reading How accurate will the Scottish independence referendum polls be?

Extreme events and probabilistic election forecasting: salutary lessons from football

In his article on last week’s forecast, John Rentoul wrote:

“Probability is hard enough to understand anyway, of course. Look at Nate Silver, the guru of American election predictions. He said Brazil had a 65 per cent chance of winning against Germany in the World Cup semi-final. Well, you could say that their 7-1 defeat fell in the other 35 per cent but – after the event – we can be pretty confident that the 65 per cent figure meant little useful.”

There are various issues here in the context of the overall article. Did the 65% figure mean little useful? How should we judge probabilistic forecasts after the event they were trying to predict? Even if John Rentoul’s interpretation here is right, should the poor performance of a football match prediction undermine the credibility of other forecasting exercises of very different kinds of events for the forecaster, or even for all forecasters? Continue reading Extreme events and probabilistic election forecasting: salutary lessons from football

Fluctuations in polls and the timeliness of the forecast

Belated thanks to John Rentoul for his excellent article on last week’s forecast. This is not to say that I necessarily agree or disagree with his views on the desirability of particular election outcomes, just that I think it is a good discussion of lots of issues in politics and forecasting. Continue reading Fluctuations in polls and the timeliness of the forecast