The Validity and Accuracy of Commonly Used Ideology Measures: A Consumer's Guide

Abstract

Are measures of legislator ideology derived from behavior accurate and valid? Past research says yes. However, the benchmarks used to reach these conclusions are often also based on legislators’ public actions. Non-ideological factors that cause legislators to take specific issue positions may be highly related across measures and mistakenly lead scholars to believe that action-based estimates are valid. This question is important because scholars frequently wish to use action-based ideology estimates as explanatory variables. Without independent validation, it is unclear whether the results of these studies are valid or the product of measurement error. Applying an ideological benchmark that is not based on legislators’ actions, I evaluate the validity of several commonly used ideology measures. The results show that action-based ideology measures produce valid estimates of legislator ideology.