Surprise me if you can: influence of newspaper endorsements in US Presidential elections

Using the daily trade of futures from the prediction markets site Intrade, we pin down the effect of printed newspapers endorsements (announcement of an explicit support for a political candidate) on the candidates' likelihood of winning. It is established that unexpected endorsements have a large impact on voters' behavior. However, we show that this effect is only true when the endorsement is a coherent one: if a newspaper that praises conservative (liberal) policies endorses a candidate with liberal (conservative) ideas, the endorsement does not impact the candidate's probability of winning, as it is regarded as incoherent. Our measure for coherence comes from Gentzkow and Shapiro (2005), but we also use Ansolabehere and Snyder (2004)'s \propensity to endorse Democrats" to show that a surprise endorsement has a large and potentially tipping effect in a tied contest