Introduction: From PSE-9 to SCAN

The final chapter of the reference manual for PSE-9 was devoted to a discussion of its limitations and uses. The point made then remains true for SCAN/PSE-10. The advantages depend upon the disadvantages. It was pointed out that if SCAN was used within its limitations the advantages would be maximised. This apparent paradox is reconsidered in the context of changes made after more than 20 years of experience.

Limiting the limitations

Some of the limitations specified in the earlier manual have been rectified in SCAN. Cognitive dysfunction and decline are now covered sufficiently for use as part of a general psychiatric examination. Most other areas previously omitted from PSE-9, but now covered by the Diagnostic Criteria for Research of subchapters F1–F5 of ICD-10, are incorporated into SCAN. F6–F9 (personality disorders, learning disability, developmental disorders and problems arising in childhood and adolescence) raise different kinds of issues and separate instruments are required to address them. Provision is made for global ratings of key items in the Clinical History Schedule. These can be used as variables in the statistical analysis. The previous symptomatic history can now be recorded in substantial detail using CAPSE-2, and a much broader range of aetiological judgements, not available in the earlier system, is now supported in SCAN-2.1.

Other limitations were solved during the subsequent development of PSE-9 itself; e.g. the addition of an Index of Definition, supporting its use in population studies and in non-hospital settings as well as for in-patients. This will be adapted for use with SCAN, once trials have provided data according to which the final structure of symptom scores can be decided. Similarly, a set of symptom-type scores will need to be developed and tested on the basis of field trials.

The provision of detailed diagnostic criteria for ICD-10 and the DSM series solved another problem, since the criteria for ICD-8 were approximated from its prose descriptions and DSM-III was not then available. However, the caveat entered for CATEGO-4 remains valid for CAPSE-2, that the computerised diagnostic categories are not intended to be regarded as a full substitute for clinical diagnosis. Only a skilled clinician can assess the degree of a patient's co-operation, cognitive ability, facility with language and other factors affecting an interview and the ratings entered into a computer.