Public opinion polls: The UK general election, 1992

The public opinion polls conducted before the 1992 general election were a statistical disaster. The errors were far in excess of expected sampling variation and can only be explained by biases specific to the context of the 1992 election since previous election results had been forecast accurately. The replication in the polls in the months before the election provides a natural experiment from which the sampling variance of quota samples can be estimated. Using a components-of-variance model, company-specific variances are estimated and are found to be consistent with those which would have been obtained from equivalent random sample designs.