The reference manual for the ninth edition of the Present State Examination (PSE-9), together with an algorithm for deriving diagnoses according to the eighth edition of the International Classification of Diseases (ICD-8), was the first edition of the PSE to be published in full (1974). It was based on 15 or more years of development and experience, culminating in the use of the seventh and eighth editions in two large international research projects – the US–UK Diagnostic Project and the WHO International Pilot Study of Schizophrenia. Because PSE-9 is brief compared with its predecessors, and a 40-item version of it can be used by trained but nonclinical interviewers for screening purposes in two-stage population surveys, it has proved very popular. A voluminous scientific literature resulted and is still accumulating. However, the advent of consensus diagnostic algorithms, in DSM-III and its successors, and the provision of an international standard in ICD-10, meant that a compatible tenth edition of the PSE must be provided. This is now implemented as the main part of the SCAN.

The points made in the preface to the reference manual for PSE-9 remain relevant for SCAN/PSE-10. In particular, the principle of top-down application of diagnostic algorithms (at that time created from the prose descriptions in ICD-8; DSM-III was still 6 years away) to a database of ratings of clinical phenomena each differentially described in a Glossary, remains fundamental. Creating each database is a joint project between interviewer and respondent, and should be independent of preconceptions about classification. The independent diagnostic rules are then applied electronically. Both processes are being immensely simplified by the use of the computer-assisted PSE (CAPSE), the results from which can also be used to inform the respondent. CAPSE provides options for the analysis and presentation of symptomatic or diagnostic profiles based on one or a series of clinical interviews with one respondent, and also for analysis of data from groups of respondents. This ease of use and choice of outputs could not have been contemplated 23 years ago.

The final sentences of the original preface will serve to end this one also. The system can be improved by dropping some of the symptoms, adding others, polishing the definitions of others and, in general, coming closer to the truth.