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	Coalition Formation Analysis	Spatial Voting Model
Field	Political Economy	Political Science
Family	MCDM	MCDM
Year of origin	1962	1957
Originator	William Riker; Michael Laver & Norman Schofield	Harold Hotelling, Duncan Black & Anthony Downs
Type	Formal theory of coalition selection	Formal model of electoral and legislative choice
Seminal source	Riker, W. H. (1962). The Theory of Political Coalitions. Yale University Press. ISBN: 9780300001754	Downs, A. (1957). An Economic Theory of Democracy. Harper & Row. ISBN: 9780060417505
Aliases	Minimal Winning Coalition Theory, Riker Size Principle, Coalition Theory, Government Coalition Analysis	Spatial Theory of Voting, Downsian Model, Proximity Voting Model, Median Voter Model
Related	4	4
Summary	Coalition formation analysis is the formal study of which subset of parties will combine to form a governing or decision-making coalition when no single party commands a majority. William Riker's 1962 The Theory of Political Coalitions supplied the foundational logic: under pure office-seeking, rational politicians form minimal winning coalitions and, by the size principle, the smallest winning coalition possible, so that the spoils of office are divided among as few partners as necessary. Michael Laver and Norman Schofield's 1990 Multiparty Government enriched this with policy-seeking motives, showing that coalitions also tend to be ideologically connected. The framework predicts coalition membership from seat shares and party positions.	The spatial voting model represents voters and political alternatives as points in a common geometric policy space and assumes that each voter supports the alternative nearest to their own ideal point. Rooted in Hotelling's location theory, Duncan Black's 1948 single-peakedness result, and Anthony Downs's 1957 economic theory of democracy, the model yields two foundational results: the median voter theorem, which identifies the equilibrium policy in one dimension, and the Downsian prediction that two vote-seeking parties converge toward the center. It is the workhorse formalism behind modern empirical estimation of political positions.