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	Foreign Policy Similarity Score	Alliance Portfolio Similarity
Field	International Relations	International Relations
Family	Process / pipeline	Process / pipeline
Year of origin	2011	1999
Originator	Foreign-policy-similarity literature (Signorino & Ritter; Voeten ideal points; Frank Häge chance correction)	Bueno de Mesquita (Tau-b); Curtis Signorino & Jeffrey Ritter (S)
Type	Dyadic measurement of revealed foreign-policy agreement	Dyadic similarity index over alliance commitment profiles
Seminal source	Häge, F. M. (2011). Choice or circumstance? Adjusting measures of foreign policy similarity for chance agreement. Political Analysis, 19(3), 287–305.	Signorino, C. S., & Ritter, J. M. (1999). Tau-b or not Tau-b: Measuring the similarity of foreign policy positions. International Studies Quarterly, 43(1), 115–144.
Aliases	Foreign Policy Similarity Measurement, UN Voting Affinity Score, Ideal Point Distance, State Preference Similarity	Alliance Portfolio Similarity Scores, S-Score of Alliance Similarity, Tau-b Alliance Similarity, Alliance Profile Similarity
Related	3	3
Summary	A foreign-policy similarity score measures how alike two states' revealed foreign-policy positions are — most commonly from their votes in the UN General Assembly, but also from alliance portfolios or treaty positions. It is a workhorse measure of shared interests, affinity, and alignment in dyadic IR. Häge (2011) shows that naive agreement and the popular S-score can be inflated by chance agreement that arises because states differ in how often they take each position, and proposes chance-corrected indices (Scott's π, Cohen's κ) that better isolate genuine alignment.	Alliance portfolio similarity measures how alike two states' overall patterns of alliance commitments are. Each state has a 'portfolio' — the profile of defense pacts, neutrality agreements, ententes, or no tie it holds with every other state — and the similarity of two portfolios is summarized in a single dyadic score. Signorino and Ritter (1999) showed that the long-dominant Kendall's tau-b measure is flawed for this purpose and introduced the S-score as a better-behaved alternative. These scores are a standard proxy for shared interests and have been used to operationalize utilities in expected-utility models of war.