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	Median Voter Model	Veto Player Analysis
分野	Political Economy	Political Science
系統	MCDM	MCDM
提唱年	1948	1995
提唱者	Duncan Black & Anthony Downs	George Tsebelis
種類	Formal model of electoral competition	Comparative institutional analysis framework
原典	Black, D. (1948). On the Rationale of Group Decision-making. Journal of Political Economy, 56(1), 23-34.	Tsebelis, G. (2002). Veto Players: How Political Institutions Work. Princeton University Press. ISBN: 9780691091891
別名	Median Voter Theorem, Black's Median Voter Theorem, Downsian Median Voter Model, Median Voter Equilibrium	Veto Players Theory, Veto Points Analysis, Tsebelis Veto Player Framework, Policy Stability Analysis
関連	4	4
概要	The median voter model is a foundational result of political economy stating that, under majority rule with voters whose preferences are single-peaked on a single policy dimension, the ideal point of the median voter is the Condorcet winner — it cannot be beaten by any other alternative in pairwise majority voting. Duncan Black established the theorem formally in 1948, and Anthony Downs extended it in 1957 into a theory of party competition in which two vote-maximizing parties converge to the median voter's preferred policy. The model is the workhorse linking the distribution of citizen preferences to equilibrium policy outcomes in democracies.	Veto player analysis is a spatial-institutional framework, developed by George Tsebelis in his 1995 article and 2002 book, for predicting the capacity of a political system to change policy. A veto player is any individual or collective actor whose agreement is required to alter the status quo. The theory shows that the potential for policy change shrinks as the number of veto players grows, as the ideological distance between them widens, and as their internal cohesion increases — three structural variables that together determine a system's policy stability independently of constitutional labels such as presidentialism or parliamentarism.