External validity of research in legal psychology.

The growth of legal psychology in the past ten or so years has been reflected in a relatively large number of edited volumes and symposia at various conventions, in the far greater visibility of psychologists in various interdisciplinary forums (such as the meetings of the American Psychology-Law Society), in the increasing frequency with which psychologists appear as expert witnesses (whose testimony addresses an ever broader range of issues), and, finally, in the founding of this journal. The main purpose of the discipline, presumably, is to explore various aspects of the interface between psychology and the law, and, more specifically, to enhance the understanding of the operation of the legal system by using psychological research methods and by testing the validity of psychological assumptions contained in legal statutes or else made by legal practitioners on an ad hoc basis. It appears self-evident that legal psychology has a strong applied orientation. Many psychologists do research in it primarily because the results of their theoretical and empirical efforts can be applied in an obviously important social domain. Many lawyers take an interest in it because they have grudgingly begun to believe that psychologists can make a practical contribution to the judicial process. Furthermore, the research emphasis has been on the various practical aspects of criminal procedure, rather than, for example, on lofty speculations about the role of psychological principles in legal doctrines; namely, a close examination of the literature in legal psychology shows that a very large proportion of all research studies falls into the