Validation of the Norwegian version of the Social Functioning Scale (SFS) for schizophrenia and bipolar disorder

Studies of social functioning in severe mental disorders are disadvantaged by the multitude of different assessment instruments in use. The present study aims to establish reliability and validity of the Norwegian version of the Social Functioning Scale (SFS) and to examine social functioning in bipolar disorder (BD) compared to schizophrenia (SZ) and healthy controls (HC). SFS, a 76 item questionnaire divided into seven subscales measuring various aspects of daily life functioning, was administered to samples diagnosed with BD (n = 100) or SZ (n = 100) and to HC (n = 100), recruited from the ongoing Tematic Organized Psychosis (TOP) study. Reliability analyses prove adequate psychometric properties both for the composite full scale score (α: 0.81) as well as for the seven subscale scores (α: 0.60-0.88). Principal component analysis of the subscales confirms a one-component structure, explaining 59% of the variance. Although significantly correlated with the Global Assessment of Functioning, our results indicate that the SFS measures different aspects of social functioning, is less influenced by demographic and clinical characteristics, but differentiates at the same time significantly BD from SZ. Thus, SFS adds valuable information as a supplement to standard clinician-rated assessment tools of social functioning, suited both for research and clinical work.