Classification in neuropsychology: a theoretical framework and research paradigm.

Classification research is not well understood in neuropsychology. A major purpose of classification research is to establish and investigate inclusion and exclusion criteria for group formation. Therefore, classification represents the foundations of clinical assessment as well as traditional contrasting groups research designs in neuropsychology. Null results in neuropsychological research do not pinpoint the basis for the absence of group differences. The most frequent research focuses on the original theory or the validity of the dependent variables. Classification research focuses on a third potential problem area, which has received little attention: poor subject classifications (invalid independent variables). The purpose of this paper is to describe a general theoretical framework and outline a set of decisions for conducting classification research in neuropsychology.