Presidential systems concentrate power because they have fewer veto players

Evidence

This choice is justified by the substantial reduction in the number of veto players within presidential systems and their intrinsic winnertake-all nature which distinguishes them from parliamentary systems22. In fact we checked that the unconditional correlation between the form of government from Presidential to Semi-presidential to parliamentary and the Freedom House index of political freedom is -.51, significant at the 1 per cent level, for the sample of countries used in Table 1 and 3 below. That is more presidential regimes are associated with lower political rights, which we interpret as a proxy for more insulation. — Philippe Aghion, Alberto Alesina, and Francesco Trebbi, Endogenous Political Institutions, 166

Categorization

• DEFINE: ‘Insulation’ is defined operationally as fewer veto players plus winner-take-all elections, proxied by low political-rights scores.
• XREF: Connects to veto-player theory (Tsebelis) and Persson & Tabellini on constitutional design.