Identification of social indicators that track changes in the human condition have been prerequisite to much of the progress of the social sciences. Early economics focused extensively on foreign trade because of the data that existed in the form of customs records. More recently, cost-of-living and unemployment indexes have played a large role in policy analyses. Now indexes of cultural and political trends are in creasingly being used. Among those that have had a major impact are Scholastic Aptitude Test scores and polls rating the president. In these instances, the existence of a usable time-series measurement has stimu lated research and analysis seeking to explain the observed results.