Developing a New Measure of Party Dominance:Definition, Operationalization and Application to 54 European Regions

Abstract

Party dominance is not clearly conceptualized and operationalized in the existing literature and has rarely been quantitatively assessed and explained. This study defines dominance as a combination of absolute dominance – the percentage of parliamentary seats won by the largest ruling party – and relative dominance, which takes into account the strength of its main competitor. Based on this definition, it would be possible to calculate an average score of party dominance over a defined period of time. The index developed here is applied to the main ruling parties in 54 regions from 1995 to 2015. Variation in regional party dominance during this period is then explained by considering dominance at the national level, differences in regional socioeconomic development and political legacies. In the last part of the article, individual party scores are aggregated by region. Association between this new aggregate score and regional quality of government is tested.