Association between Global Assessment of Functioning scores and indicators of functioning, severity, and prognosis in first-time schizophrenia

Background: Assessment of psychosocial functioning in people with schizophrenia is important. The Global Assessment of Functioning (GAF-F) scale represents a widely applied, easy, and quick tool, but its validity and reliability have been debated. The aim was to investigate whether GAF-F scores are associated with other indicators of functioning, severity, and hospitalization. Methods: A Danish population-based cohort study of adults (>= 18 years) with a recorded GAF-F score at first-time schizophrenia diagnosis during 2004-2011 was performed. The internal validity of GAF-F was evaluated by assessing its association with other baseline measures of functioning and illness severity. Risk of schizophrenia hospitalization within 2 years was evaluated using Cox regression stratified by sex and adjusted for age, year of diagnosis, and inpatient/outpatient status at diagnosis. Results: We identified 2,837 cases of schizophrenia with a GAF-F score at first-time diagnosis (73.0% inpatients; 62.6% males). GAF-F was associated with several baseline measures of functioning and illness severity, such as female sex, being in work, and a longer baseline hospitalization. Lower GAF-F scores were associated with higher hospitalization risk among males (reference GAF-F 61-100): GAF-F 51-60: hazard rate ratio (HRR) = 1.24 (95% confidence interval [CI] = 0.89-1.75); GAF-F 41-50: HRR = 1.31 (95% CI = 0.97-1.77); GAF-F 31-40: HRR = 1.36 (95% CI = 1.01-1.82); GAF-F 21-30: HRR = 1.50 (95% CI = 1.09-2.06); and GAF-F 1-20: HRR = 2.30 (95% CI = 1.36-3.90), fitting a dose-response relationship (P= 0.031). This association was not found in females. Conclusion: GAF-F at first-time schizophrenia diagnosis showed good internal validity against other measures of functionality in a Danish hospital setting. Severe impairment (as measured by the GAF-F score) at first-time schizophrenia diagnosis was associated with a higher risk of 2-year hospitalization among males, which may indicate sex differences in the course of disease and treatment response.