Compare methods

	Ideal Point Estimation	Roll-Call Analysis
Field	Political Science	Political Science
Family	Latent structure	Latent structure
Year of origin	2004	—
Originator	Clinton, Jackman & Rivers (Bayesian formulation); Poole & Rosenthal (spatial tradition)	Spatial-voting tradition; Poole, Rosenthal, Clinton, Jackman, Rivers
Type	Latent-variable spatial model of binary choice data	Scaling and analysis of legislative binary-choice data
Seminal source	Clinton, J., Jackman, S., & Rivers, D. (2004). The Statistical Analysis of Roll Call Data. American Political Science Review, 98(2), 355–370.	Poole, K. T. (2000). Nonparametric Unfolding of Binary Choice Data. Political Analysis, 8(3), 211–237.
Aliases	Ideal point model, Item response theory for roll calls, Spatial voting model, Bayesian ideal points	Roll call voting analysis, Legislative vote scaling, Roll-call scaling, Optimal classification of votes
Related	4	3
Summary	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.	Roll-call analysis is the study of recorded legislative votes to recover the structure of political conflict — the ideological positions of legislators, the dimensionality of the issue space, and the cohesion of parties. It encompasses parametric spatial and item-response models that estimate latent ideal points, nonparametric scaling such as optimal classification that maximizes correctly classified votes without distributional assumptions, and descriptive cohesion statistics like the Rice index. Together these tools turn a matrix of yea/nay votes into a map of who agrees with whom and why.