The principles underlying the creation and long-term development of the Present State Examination (PSE), now incorporated, with its glossary of definitions of symptoms and other components, in a shell known as the Schedules for Clinical Assessment in Neuropsychiatry (SCAN), are derived from standards of clinical assessment gradually developed from the late 18th century onwards. A form of ‘mental state examination’ is now an established part of the standard curriculum in most medical schools. To conduct such an examination requires the clinician to meet a demanding list of requirements. The first essential is a sound grasp of clinical psychopathology. This confers an ability to recognise, and distinguish within and between, an extensive range of symptoms, such as delusions, hallucinations, obsessional ruminations, irrational fears of harmless stimuli and feelings of excessive guilt. A technique of ‘cross-examination’, based on the glossary of differential definitions of symptoms, must be learned in the first place by observing experienced practitioners interviewing their patients. It is only after completing a comprehensive clinical symptom base that diagnostic procedures should, if needed, be brought into play with the help of algorithms laid down in international standards, as well as those of any other system in local use. These specifics differentiate SCAN from methods such as fully structured questionnaires or self-report forms, which have other purposes.
The aims of SCAN
The three central aims of SCAN can be summarised very simply, in one sentence. They are to provide comprehensive, accurate and technically specifiable means of describing and classifying clinical phenomena in order to make comparisons. Making comparisons is at the heart of all clinical, educational and scientific activities.
The first, clinical, aim is to promote and use high-quality clinical observation. The PSE is designed to allow comparison of each respondent's experiences and behaviour against the examiner's glossary-defined concepts by a process of controlled clinical ‘cross-examination’. The resulting outputs in the form of single symptoms, profiles, scores and rule-based categories of disorder can be compared with each other wherever in the world they are elicited. Thus, they can be used as a comparable base for clinical audit, needs assessment and monitoring the progress of individual respondents. It is essential to understand that the SCAN database is not tied exclusively to systems such as ICD–10 (World Health Organization, 1992) or DSM–IV (American Psychiatric Association, 1994).