Political stock markets and unreliable polls

A political stock market (PSM) clearly beat the polls in predicting the outcome of a Swedish referendum on whether or not Sweden should join the European Union. In fact, polls were unable to make such predictions since the number of undecided respondents always far exceeded the observed YES/NO margin. However, an obstacle to PSMs serving as a superior forecasting instrument is that they can be sensitive to price distortions - by interest groups that may wish to effectuate, and pay for, such distortions - or forecast competitions tied to PSM trade gains, the latter of which was tested here.