Bandwagon, Underdog, or Projection? Opinion Polls and Electoral Choice in Britain, 1979–1987

Since the widespread use of opinion polls in British general elections began in the 1950s, there has been continuing controversy concerning their impact on the vote. The bandwagon effect sees voters favoring a party that is doing well in the polls, while the underdog effect predicts that support will go to a party trailing in the polls. There is also the possibility of a projection effect, with voters expectations conforming to their partisanship. The results presented here, applying logistic regression to “exit poll survey data collected during the 1979, 1983, and 1987 British general election campaigns, find some evidence of a bandwagon effect in all three elections, but no evidence of an underdog effect and only minor evidence of a projection effect. However, there is a consistent interaction between poll influence and those who decided which way to vote during the election campaign, suggesting that opinion polls can facilitate tactical voting, especially in three-party competition.