Opinion poll
1992 UK general election

An oft-quoted example of opinion polls succumbing to errors occurred during the 1992 UK general election. Despite the polling organizations using different methodologies, virtually all the polls taken before the vote, and to a lesser extent exit polls taken on voting day, showed a lead for the opposition Labour Party, while the actual vote gave a clear victory to the ruling Conservative Party. In their deliberations after this embarrassment, the pollsters advanced several ideas to account for their errors, including:

The relative importance of these factors was, and remains, a matter of controversy. Polling organizations have since then adjusted their methodologies and have achieved more accurate results in subsequent election campaigns. A comprehensive discussion of these biases and how they should be understood and mitigated is included in several sources including Dillman and Salant (1994).
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