The apparent heterogeneity of some disorders according to the Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM–IV; American Psychiatric Association, 1994) is not limited to Axis I disorders. Fossati et al. (2005) compared several different factor structures for the schizotypal personality disorder (SPD) criteria and found that a three-factor model (Cognitive-Perceptual, Interpersonal, and Disorganization) fit best. Intercorrelations among the three factors ranged from .14 to .63, again indicating substantial unshared variance in each factor. Here, too, individuals can be high on one factor but not on another, raising the question of the coherence of SPD as a psychological construct. Again in this case, the same quantitative symptom count could reflect different dysfunctional experiences.
