Development and psychometric performance of the schizophrenia objective functioning instrument: an interviewer administered measure of function.

Existing measures for functional assessment do not adequately address the relationship between cognitive impairment and function. The Schizophrenia Outcomes Functioning Interview (SOFI) was developed to measure community functioning related to cognitive impairment and psychopathology. Following review of existing measures and discussion with experts, caregivers, and patients, content was generated for four domains: 1) living situation; 2) IADLs; 3) productive activities; and 4) social functioning. The final SOFI was constructed with items informing domain scores, and an interviewer-completed global rating for each domain. Psychometric characteristics of the SOFI were evaluated in a sample of 104 community residing patients with schizophrenia and their informants. Test-retest reliability was evaluated in a sub-sample of patient-informant dyads using ICC; all values were >0.70 for both patient-interviews (SOFI-P) and informant-interviews (SOFI-I). Inter-rater reliability ICCs ranged from 0.50 to 0.79 on a different sub-sample. The SOFI demonstrated adequate construct validity based on correlations with the PSP (range 0.58 to 0.76; p<0.0001) and the QLS (p<0.001). Some correlations between SOFI and PETiT scores were low to moderate (p<0.05). Discriminant validity was supported based on SOFI score comparisons for patient groups based on PANSS and BACS scores (p<0.05); SOFI scores differed between borderline and moderately ill patients as measured by the CGI-S (p<0.05). The SOFI expands on existing measures and more comprehensively captures functioning of patients in the real world than other performance-based (proxy) measures. The SOFI has good evidence supporting reliability and construct validity, and may be a useful measure of functional outcomes in schizophrenia.