Why Were the UK Election Polls So Wrong? A Statistical Mystery

Last Thursday the UK’s Conservative Party stomped to an electoral victory that fairly shocked the country. The Tories won a comfortable majority of seats in parliament, enabling them to govern the nation without a coalition partner. That result contrasted sharply with the pre-election polls, which (on average) predicted a dead heat between the Conservatives and their long-time rivals in the Labor Party, each one projected to net 33.6 percent of the vote. The substantial error has provoked much hand-wringing among British pollsters, whose industry organization is conducting an official review of the fiasco.

So what did really go wrong? Nearly a week out, no one seems to have come up with a convincing answer, though a range of potential explanations—some connected, some mutually exclusive—have emerged. In an era when statistical analysis is coming to ever greater importance to fields as diverse as politics, finance,