Measurement Identity in the Longitudinal Analysis of Legislative Voting

Recent advances in data processing technology have made it possible for the political scientist to extend the coordinates of his research space across political systems as well as through time. Without the present-day capacity to retrieve and process speedily the large banks of data accumulated through comparative analyses, such studies would be prohibitively time-consuming, and probably not done at all. As it is the technical hurdles are diminishing in importance, only to be replaced in our attention by the methodological barriers to comparative analysis. In this paper the focus is on one of the basic problems of comparative analysis: the achievement and validation of measurement identity.Measurement identity refers to the content equivalence of two or more measures and is a key consideration in comparative studies whether the comparison is cross-cultural or historical. Unless there are clear indications of the identity of the measures on which the comparisons are based, such comparisons are meaningless. For the political scientist engaged in cross-cultural research, the problem of measurement identity virtually thrusts itself upon him, since he is already sensitive to differences between culturally different political systems. In contrast, the historical researcher who is working within a single cultural context, and is attuned to the continuity of historical themes, may neglect the measurement identity requirements of his research. The purpose of this paper is to give visibility to this measurement issue as it confronts historical research in the field of legislative behavior. My specific referent is the longitudinal study of legislative voting behavior.