Do Populists Win on Facebook? The Engagement Premium of Populist Parties in Europe, 2010 to 2020

Do populist parties get more attention on Facebook than other parties, and is that true everywhere? I use 669,760 posts from 112 official party pages in 17 European countries, posted between January 2010 and September 2020, with 186,939 posts from 74 party leaders as a second sample. I classify parties as populist, far right or far left using the PopuList, an expert classification, year by year, and add vote shares and government membership from ParlGov. I compare each post with posts by other parties in the same country and month. A typical post by a populist party received about 2.5 times as many likes, comments, shares and reactions as a post by another party of the same size and government status. Populist radical left parties had the largest premium (about 5.4 times), populist radical right parties about 2.3 times and other populists about 1.5 times. I find no premium for far-left parties that are not populist, and no separate premium for Euroscepticism. The premium differs a lot between countries: it was large in Spain, the United Kingdom, Norway, Sweden, Hungary and France, and I cannot detect it in Slovenia, Luxembourg, Slovakia, Finland, Greece or Switzerland. Bigger audiences account for more than half of it. Populist pages had about 1.9 times the page likes of other parties with the same vote share, but at equal page size a premium of about 1.5 times remained. Populist posts drew a higher share of angry reactions (4.4% against 2.7% of interactions). I find no detectable change in the premium after Facebook's January 2018 News Feed change.