Definition and prevalence of severe and persistent mental illness

Background There is little consistency in how severe mental illness (SMI) i s defined in practice, and no operational definitions. Aims To test two operationalised definitions, based on the National Institu te of Mental Health (1987) definition: the first uses three criteria (diagn osis of psychosis; duration of service contact greater than or equal to 2 y ears; GAF score less than or equal to 50), the second only the last two. Method Annual prevalence rates of SMI in two European catchment areas for e ach criterion and the criteria combined were calculated. Results The first definition produced rates of 2.55 and 1.34/1000 in London and Verona, respectively; the second permitted an additional 0.98/1000 non psychotic disorders to be included in Verona. Conclusions The three-dimensional definition selects a small group of patie nts with SMI who have psychotic disorders. The two - dimension al approach al lows estimates of SMI prevalence rates which include all forms of mental disorder. Declaration of interest Funding provided by the University of Verona and th e Bethlem and Maudsley NHS Trust.