Accuracy of Pre-election Polls for the 2006 Italian Parliamentary Election: Too Close to Call

In this article, we analyze the accuracy of over 70 published and 19 unpublished preelection polls reporting results pertaining to the April 2006 election for the Chamber of Deputies in Italy and apply a new measure of predictive accuracy, A, recently introduced in the U.S. context. The center-left coalition won the election with a narrow margin of 0.1 percent of the votes, which came as a surprise: all published pre-election polls had attributed a 3 to 4 percentage point lead for the center-left. The failure of virtually all pollsters to predict the outcome is due to various factors: sampling error issues; a 15-day pre-election embargo on publishing results; high coverage error due to households having only mobile phones or no phone at all; a possible reluctance of Italian voters to declare their intention to vote for the center-right. The new measure of poll accuracy was easy to adapt and apply to the Italian context, due to a recent election reform. Information given by pollsters remains, however, too inadequate to engage in comprehensive evaluations of their polls.