The measurement of populist attitudes: Testing cross-national scales using item response theory

Recent research in the populism literature has devoted considerable efforts to the conceptualisation and examination of populism on the individual level, that is, populist attitudes. Despite rapid progress in the field, questions of adequate measurement and empirical evaluation of measures of populist attitudes remain scarce. Seeking to remedy these shortcomings, we apply a cross-national measurement model, using item response theory, to six established and two new populist indicators. Drawing on a cross-national survey (nine European countries, n = 18,368), we engage in a four-folded analysis. First, we examine the commonly used 6-item populism scale. Second, we expand the measurement with two novel items. Third, we use the improved 8-item populism scale to further refine equally comprehensive but more concise and parsimonious populist measurements. Finally, we externally validate these sub-scales and find that some of the proposed sub-scales outperform the initial 6- and 8-item scales. We conclude that existing measures of populism capture moderate populist attitudes, but face difficulties measuring more extreme levels, while the individual information of some of the populist items remains limited. Altogether, this provides several interesting routes for future research, both within and between countries.