Published online by Cambridge University Press: 04 January 2017
Research designs that call for the estimation of time trends in legislator ideal points must allow for changes in underlying policy spaces. Simply put, a set of legislator ideal points from one such space cannot necessarily be compared with a set of ideal points from another. Rothenberg and Sanders's (2000, American Journal of Political Science 44:316–325) analysis of shirking in Congress does not internalize this point insofar as it assumes that legislator ideal points from adjoining congressional sessions lie in a common space. While it may be the case that members of Congress shirk ideologically when approaching retirement, the regression estimates at the heart of Rothenberg and Sanders neither support this possibility nor constitute evidence against it.