New forecasting methods.
Photographer: Leon Neal/AFP/Getty Images
Back in late 2016, following a year of political upsets, I argued here that political polling and forecasting wasn’t dead but needed to adapt. Fast forward a little over a year, and change is already apparent.
Polls in the U.K. badly missed in the 2015 general election, showing a tied result when then Conservative Prime Minister David Cameron’s emerged with a six-and-a-half point margin of victory. They wrongly predicted a Remain victory in the 2016 referendum on European Union membership and were wildly off-target again in the 2017 general election. In the U.S., state polls – particularly in states where whites without college degrees are numerous – missed key swing state victories for Donald Trump in 2016.
Although the magnitude of polling misses hasn’t changed much over time, the number of close, high-stakes contests has increased the risk of a bad call on a major vote. This matters especially in the U.K., because in a winner-takes-all electoral system (as opposed to one that uses proportional representation) even modest errors in the popular vote translate into much larger errors in the share of seats won.