Comparing Nominate and Ideal: Points of Difference and Monte Carlo Tests

46 Pages Posted: 6 Oct 2008

See all articles by Royce Carroll

Royce Carroll

University of Essex - Department of Government; Rice University - Department of Political Science

Jeffrey B. Lewis

University of California, Los Angeles (UCLA)

James Lo

University of California, Los Angeles (UCLA) - Department of Political Science

Keith T. Poole

University of Georgia - School of Public and International Affairs

Howard Rosenthal

New York University

Date Written: September 30, 2008

Abstract

Empirical models of spatial voting allow legislators' locations in an abstract policy or ideological space to be inferred from their roll call votes. Over the past 25 years, these models have provided new insights about the US Congress and legislative behavior more generally (see, for example, Poole and Rosenthal, 1997). There are now a number of alternative models, estimators, and software that researchers can use to recover latent issue or ideological spaces from voting data. While these different estimators usually produce substantively similar estimates, important differences also arise. In this paper, we investigate the sources of observed differences between two leading methods, NOMINATE and IDEAL. Considering data from the 1994 to 1997 Supreme Court and the 109th Senate, we demonstrate that while some observed differences in the estimates produced by each model stem from fundamental differences in their underlying behavioral assumptions, others arise from arbitrary differences in implementation. Using Monte Carlo experiments, we find that neither model has a clear advantage over the other in the recovery of legislator locations or roll call midpoints in either large or small legislatures.

Keywords: NOMINATE, IDEAl, spatial voting, roll call votes, ideal points

Suggested Citation

Carroll, Royce and Lewis, Jeffrey B. and Lo, James and Poole, Keith T. and Rosenthal, Howard, Comparing Nominate and Ideal: Points of Difference and Monte Carlo Tests (September 30, 2008). Available at SSRN: https://ssrn.com/abstract=1276007 or http://dx.doi.org/10.2139/ssrn.1276007

Royce Carroll

University of Essex - Department of Government ( email )

Wivenhoe Park
Colchester CO4 3SQ, CO4 3SQ
United Kingdom

Rice University - Department of Political Science ( email )

MS-24
P.O. Box 1892
Houston, TX 77251-1892
United States
713-348-2103 (Phone)
772-264-8530 (Fax)

HOME PAGE: http://rcarroll.web.rice.edu

Jeffrey B. Lewis

University of California, Los Angeles (UCLA) ( email )

405 Hilgard Avenue
Box 951361
Los Angeles, CA 90095
United States

James Lo

University of California, Los Angeles (UCLA) - Department of Political Science ( email )

Loas Angeles, CA
United States

Keith T. Poole (Contact Author)

University of Georgia - School of Public and International Affairs ( email )

Baldwin Hall
Athens, GA 30602-6254
United States

Howard Rosenthal

New York University ( email )

19 W 4th St
New York, NY New York 10012
United States
4155199591 (Phone)
4155199591 (Fax)

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