I. Introducing a New Instrument for Rating Observed Behaviour∗ and the Rationale of the Psychological Impairment Concept

Based on the experience with the International Pilot Study on Schizophrenia (IPSS) (WHO 1973, 1979), the WHO Division of Mental Health and Centres in Sofia, Groningen and Mannheim, joined by expertise from Nottingham and Zurich, conceived a prospective study to assess the ‘natural history’ (Ciompi, 1980a, b; Watt et al, 1983; Biehl, 1987) of psychological impairments and social disabilities in patients with functional psychosis in different socio-cultural environments (Jablensky et al 1980).