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More than a decade ago, a series of retrospective studies examined the concordance between proliferating definitions of severe psychiatric disorder. The European response has been a poly-diagnostic one, which has attempted to maintain interest in a broad range of psychiatric phenomena in the psychoses. In North America a more convergent approach has emerged, resulting in a series of operational definitions evolving from one another, and a correspondingly limited capacity to allow alternative perspectives to co-exist. The present study uses a prospective design as well as recent improvements in the clinical validity of psychopathology assessment to re-evaluate the relationships between competing concepts of psychotic illness in a broad sample (N = 176) of recent-onset psychotic patients. In the schizophrenic group, concordance was predictably highest among recent North American 'cousins', and lowest among various historical concepts. There was a moderately high concordance between selected schizoaffective and atypical psychosis definitions, indicating that this component is an important area for further studies of descriptive validity. These interrelationships may be used as a starting point to explore latent classes underlying the phenomena of functional psychosis.

The Royal Park Multidiagnostic Instrument for Psychosis is a validity-oriented assessment procedure developed for the acute psychotic episode using serial interviews and multiple information sources. This article describes the development and structure of the RPMIP and reports the findings of an interrater reliability study (n = 50). In addition, results are presented from a study that examined aspects of the procedural validity of the instrument when contrasted with consensus diagnoses made by a team of clinicians applying operational criteria in a less formal way to a common sample of patients (n = 87). Finally, the role of assessment procedures of this type in research into psychiatric disorders is briefly discussed.