Replication Data for: The state of populism: Introducing the 2023 wave of the Populism and political parties expert survey

To understand the evolution of party-based populism, reliable and valid measurement is essential. This article presents the second wave of the Populism and Political Parties Expert Survey, capturing populism with a continuous, five-item multidimensional latent construct in 312 political parties across 31 European countries in 2023. We validate the approach through Exploratory Factor Analysis (EFA), Confirmatory Factor Analysis (CFA) and Item Response Theory (IRT). The IRT findings confirm the discriminatory power of the five items, while CFA results establish strict measurement invariance from 2018 to 2023, supporting cross-temporal comparisons. Substantively, we show that radical right parties remain the most populist, followed by the radical left, with both nativism and left-wing economic stances as robust predictors of populism. Overall, average populism levels declined from 2018 to 2023, largely due to decreases among parties with weaker nativist and authoritarian tendencies.