Assessing the presidentialisation thesis: Prime ministerial authority in an era of rising centralisation and personalisation

Abstract The ‘presidentialisation’ of prime ministers has become a prominent theory in political science, particularly within the study of executive politics. The central claim that prime ministers and their agents exert increasing authority over government has sparked considerable definitional and theoretical debate. Empirical testing, however, has largely been limited to case studies of individual leaders and countries. Using a reliable metric for prime ministerial power across 21 countries over 40 years, we provide a large-N testing of the thesis. Our analysis finds no secular trend towards increasing prime ministerial power. In some countries, we observe a sharp decline in prime ministerial control over policy, potentially linked to the fragmentation of party systems in Western democracies. At the same time, the data point to a broader trend toward centralisation and personalisation, suggesting that the growing focus on leaders is subtly and profoundly transforming the exercise of executive power in contemporary democracies. The findings indicate that caution is warranted about unidirectional claims of presidentialisation.