Compare methods

	Multidimensional Unfolding	Ideal Point Estimation
Field	Political Science	Political Science
Family	Latent structure	Latent structure
Year of origin	2000	2004
Originator	Keith T. Poole (nonparametric optimal classification and unfolding)	Clinton, Jackman & Rivers (Bayesian formulation); Poole & Rosenthal (spatial tradition)
Type	Latent-space scaling model placing individuals and stimuli in a joint space	Latent-variable spatial model of binary choice data
Seminal source	Poole, K. T. (2000). Nonparametric Unfolding of Binary Choice Data. Political Analysis, 8(3), 211–237.	Clinton, J., Jackman, S., & Rivers, D. (2004). The Statistical Analysis of Roll Call Data. American Political Science Review, 98(2), 355–370.
Aliases	Unfolding analysis, Optimal classification, Preference unfolding, Joint-space scaling	Ideal point model, Item response theory for roll calls, Spatial voting model, Bayesian ideal points
Related	5	4
Summary	Multidimensional unfolding places both individuals and the stimuli they evaluate — candidates, parties, bills — in a single joint low-dimensional space, so that each person's preferences are explained by their proximity to the stimuli. In political science it underlies Keith Poole's nonparametric optimal classification of roll-call votes and the unfolding of thermometer ratings and rank orders, recovering legislators' and bills' positions from nothing but the pattern of choices. Unlike correlation-based scaling, unfolding treats preference as a single-peaked function of distance: you like what is close to you and dislike what is far.	Ideal point estimation recovers the latent policy positions — ideal points — of political actors from their observed binary choices, most often legislators' yea/nay votes on roll calls. Building on the spatial theory of voting and formalized as a Bayesian item-response model by Clinton, Jackman, and Rivers in 2004, it places each legislator and each bill in a low-dimensional policy space and estimates positions so that the probability a legislator votes yea increases as the bill's 'yea' outcome moves closer to that legislator's ideal point.