Abstract
BACKGROUND AND OBJECTIVE: Recent developments in Europe and Portugal provide a fertile ground for the rise of populism. Despite the growing interest in the topic, there is no reliable tool to gauge Portuguese citizens' populist attitudes to date. The Populist Attitudes Scale (POP-AS), developed by Akkerman et al. [1], is one of the best-known instruments for measuring populist attitudes. However, no version for use in the Portuguese population is available. This paper describes the psychometric validation of the POP-AS for the Portuguese population. METHODS: Trustworthy measures of validity suggested by Boateng et al. [2] to address the psychometric features of the POP-AS were approached. A robust psychometrical pipeline evaluated the reliability, construct validity, cross national/educational validity, and internal validity of the POP-AS. RESULTS: The Portuguese version of the POP-AS exhibited sound internal consistency and demonstrated adequate properties of validity: a one-factor model was obtained, revealing evidence of construct validity; invariance was ensured for education and partially ensured for the country; All the items of the POP-AS revealed relatively good values of discrimination and contributed adequately to the total score of the scale, ensuring evidence of internal validity. CONCLUSION: Psychometric analysis supports the POP-AS as a valid and reliable instrument for measuring populist attitudes among Portuguese citizens. A validation framework for measurement instruments in political science was proposed. Implications of the findings are discussed.