Research has demonstrated considerable heterogeneity in the long-term course of schizophrenia. In the period preceding the onset of frank psychosis (onset), patients vary relative to the rapidity of onset, the presence or absence of asociality, and the presence or absence of semipsychotic symptoms. Following the onset of psychosis (middle course), patients may suffer from episodic or unremitting psychosis, and may or may not exhibit the deficit syndrome. In late adult life (late course), patients vary relative to the presence or absence of an improvement in psychosis and social capability.

The usual approach to the study of putative course subtypes is to define a subtype by a number of features; they may include features of more than one epoch. In addition, the course of psychosis has not been distinguished from enduring personality impairments in these subtypes. Another approach to defining putative course subtypes would be based on dichotomizing patients according to the presence or absence of a particular feature of a single epoch. This second approach has important advantages: the availability of larger study populations and a diminished liability for confounding due to the correlates of features other than those under scrutiny.