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Democracy as a Latent Variable


  • Earlier versions of this work were presented at the 2003 annual meeting of the Midwestern Political Science Association, 2003 annual meeting of the Society for Political Methodology, and the 2003 annual meeting of the American Political Science Association. We thank Larry Bartels, Neal Beck, Jon Bendor, Bruce Bueno De Mesquita, Alberto Diaz, Jim Fearon, William Jacoby, Steve Krasner, David Laitin, Jeffrey Lewis, Nikolay Marinov, Andrew Martin, Doug Rivers, and Mike Tomz for useful comments and references. Errors and omissions remain our own responsibility.

Shawn Treier is assistant professor of political science, University of Minnesota, 1414 Social Sciences Building, 267 19th Avenue South, Minneapolis, MN 55455 ( Simon Jackman is professor of political science, Stanford University, 616 Serra St., Encina Hall West, Room 100, Stanford, CA 94305-6044 (


We apply formal, statistical measurement models to the Polity indicators, used widely in studies of international relations to measure democracy. In so doing, we make explicit the hitherto implicit assumptions underlying scales built using the Polity indicators. Modeling democracy as a latent variable allows us to assess the “noise” (measurement error) in the resulting measure. We show that this measurement error is considerable and has substantive consequences when using a measure of democracy as an independent variable in cross-national statistical analyses. Our analysis suggests that skepticism as to the precision of the Polity democracy scale is well founded and that many researchers have been overly sanguine about the properties of the Polity democracy scale in applied statistical work.