Does fake news affect voting behaviour?

We study the impact of fake news on votes for populist parties in the Italian elections of 2018. Our empirical strategy exploits the presence of Italian- and German-speaking voters in the Italian region of Trentino Alto-Adige/Südtirol as an exogenous source of assignment to fake news exposure. Using municipal data, we compare the effect of exposure to fake news on the vote for populist parties in the 2013 and 2018 elections. To do so, we introduce a novel indicator of populism using text mining on the Facebook posts of Italian parties before the elections. We find that exposure to fake news is positively correlated with vote for populist parties, but that less than half of this correlation is causal. Our findings support the view that exposure to fake news (i) favours populist parties, but also that (ii) it is positively correlated with prior support for populist parties, suggesting a self-selection mechanism.