Methodology for identifying specific psychological deficits: introduction to the special section.

A long-standing problem in psychopathology research is establishing that patterns of differences between groups reflects differences of underlying constructs and not artifacts of research design, measurement, or analysis. This introduction provides a context for 4 articles that consider several controversial issues regarding this problem and presents a précis. Although these articles focus on schizophrenia, it is noted how the issues are of more general relevance to psychopathology researchers.