The PopulisTree: A systematic taxonomy and dataset to study populist parties in Europe

The Popu-List is an essential tool for identifying populist parties, but it does not provide a comprehensive analysis of their ideological varieties. This article introduces the PopulisTree, a taxonomy that systematically classifies populist actors into five main types—populist right, left, agrarian, regionalist, and valence—as well as more specific sub-types, including the populist radical right. The taxonomy's utility is demonstrated through its application to the 2024 European Parliament (EP) elections and the development of the PopulisTreeEU dataset, which provides information on the ideology, votes, seats, and EP political groups of populist parties in EP elections since 1979. Furthermore, in its dedicated website, the PopulisTree taxonomy is applied to all the parties included in the Popu-List, enabling its adoption for the study of national elections.