Comparative scholars on systems of government have argued that the concentration of executive decision-making powers in the hands of the chief executive is a distinctive feature of presidential systems, while a joint decision-making process would be the standard in parliamentary democracies. In this study, we challenge these arguments, and we aim to answer the following questions: Is vertical dominance from the top (president) to the bottom (cabinet ministers) a premise of the executive decision-making process in presidential systems? Is a collegial or joint executive decision-making process the premise of parliamentary systems? Regarding the relationship between the chief executive and the cabinet ministers, would the differences between these systems of government be rigid or do they share similar structures? By analyzing constitutions regulating the executive decision-making process in 82 democracies, we develop a new index on the dominance of the chief executive over the cabinet. We argue that the degree of power sharing between chief executives and cabinet ministers should be considered on a continuum scale and that the level of dominance of the chief executive over cabinets varies from a centralized structure to a decentralized structure in both of these systems of government. Our results suggest that the elements presented in theoretical models that try to explain the formal sharing of power in parliamentary systems can also be used to understand presidential systems. Our results reveal that, when comparing dichotomous models on power sharing and policy-making across different systems of government, executive decision-making processes can share similar structures.
