Policymakers are increasingly interested in knowing, in specific terms, the value and outcomes of public investment in science and technology and the subsequent contribution of this investment to economic growth. In 1993, RAND conducted a literature review concerning performance goals for science, methods for tracking and monitoring science, and methods for identifying where the U.S. should maintain "preeminence" in science. Researchers used a number of bibliometric tools, including publication and citation counts and co-word and co-citation analysis, which provide usable data on the state of a nation's scientific enterprise. They also found literature on patent counts and analysis, technology balance of payments, and the awarding of international prizes as indicators of strength in science. None of these techniques, however, provides a full picture of the state of U.S. science, either at an aggregate or the disciplinary level. Analysis of data using these methods, coupled with a thorough review by an expert panel of research practitioners and users, may provide some insight into the standing of U.S. science relative to the rest of the world. But measures of science are imperfect, and without a theoretical framework within which to place the results of the assessment of science, it is difficult to know how well or poorly a nation's scientific activity is being measured and compared.