Methodological considerations in the use of attribute variables in neuropsychological research.

This paper examines the conceptual and statistical difficulties created when neuropsychological research uses attribute variables in traditional orthogonal experimental designs. It is argued that attribute variables, as a result of their statistical and theoretical nonindependence, break the underlying assumptions of these traditional designs, and may lead to incorrect inferences being drawn. These difficulties are illustrated in a consideration of the typical use of analysis of variance designs, matched groups designs, and the analysis of covariance. Finally, a plea is made for the explicit consideration of the assumptions underlying the design models used in neuropsychological research, and a suggestion is made regarding the more appropriate use of correlational techniques in neuropsychology.