How Accurate Have Political Election Polls Been Historically?

Historically, political polling has typically predicted the winner of a given election with great accuracy, although polls have been incorrect in certain races. However, as cellphone use has become more pervasive and people have grown less willing to answer polling questions, polling accuracy has suffered.

Because the entities conducting polls have a harder time contacting those who are not using landline telephones, and individuals whom those entities are able to contact are increasingly refusing to participate, the ability of polling to predict opinions and probability for certain segments of society to turn out to vote has diminished. As a result, polling in recent elections, such as in both the U.S. midterm elections and the United Kingdom general election in 2014, have inaccurately predicted outcomes.