On the use of scaling and clustering in the study of semantic deficits.

In the past decade, several studies have used scaling and clustering techniques to document semantic storage deficits in patients with Alzheimer's disease and in schizophrenia. In this article the authors argued that many of the conclusions drawn from these studies are unjustified by the data. They reviewed the methodology used in these studies and presented data from simulation studies to further investigate the validity of their conclusions. The authors elaborate on the criteria needed to exclude alternative accounts of the data and present empirical data from patients with Alzheimer's disease and normal control participants to demonstrate that analyses of the patients' proximity data do not provide unambiguous evidence for a generalized semantic storage deficit.