Spatial Models of Parliamentary Voting

This book presents a simple geometric model of voting as a tool to analyze parliamentary roll call data. Each legislator is represented by one point and each roll call is represented by two points that correspond to the policy consequences of voting Yea or Nay. On every roll call each legislator votes for the closer outcome point, at least probabilistically. These points form a spatial map that summarizes the roll calls. In this sense a spatial map is much like a road map because it visually depicts the political world of a legislature. The closeness of two legislators on the map shows how similar their voting records are, and the distribution of legislators shows what the dimensions are. These maps can be used to study a wide variety of topics including how political parties evolve over time, the existence of sophisticated voting and how an executive influences legislative outcomes.

1. Introduction; 2. The geometry of parliamentary roll call voting; 3. The optimal classification method; 4. Probabilistic spatial models of parliamentary voting; 5. Practical issues in computing spatial models of parliamentary voting; 6. Conducting natural experiments with role calls; 7. Conclusion.

Presents a geometric voting model for analyzing parliamentary roll call data. The model can be used to study various topics related to legislative voting, including how political parties evolve over time, the existence of sophisticated voting, the representation of ethnic minorities in the legislature, and constituency interests and legislative behavior.

Keith T. Poole is a Professor of Political Science at the University of California, San Diego. He is the author or coauthor of over 40 articles as well as the coauthor of Congress: A Political-Economic History of Roll Call Voting and Income Redistribution and the Realignment of American Politics.