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Shy Tory Factor is a name given by British opinion polling companies to a phenomenon observed in the 1990s, where the share of the vote won by the Conservative Party (i.e. the 'Tories') in elections was substantially higher than the proportion of people in opinion polls who said they would vote for the party.

In the 1992 general election, the final opinion polls gave the Conservatives between 38% and 39% of the vote, about 1% behind the Labour Party. In the final results, the Conservatives had a lead of 7.6% over Labour. As a result of this failure to 'predict' the result, the Market Research Society held an inquiry into the reasons why the polls had been so much at variance with actual public opinion. The report found that 2% of the 8.5% error could be explained by Conservative supporters refusing to disclose their voting intentions; it cited as evidence the fact that exit polls on election day also underestimated the Conservative lead, when polls could not be affected by sampling error.

After the 1992 election, most opinion pollsters altered their methodology to try to correct for this observed behaviour of the electorate. The methods varied for different companies. Some adopted the tactic of asking their interviewees how they had voted at the previous election, and then assumed that those who had voted Conservative before but were now "unsure" (or simply not answering) would indeed again vote Tory. Others weighted their panel so that their past vote was exactly in line with the actual result of the election. For a time, opinion poll results were published both for unadjusted and adjusted methods.

However, with the Labour Party under Tony Blair now in power for the last 10 years, The Guardian newspaper has recently mused about the emergence of the Shy Labour Voter.[1]