Reliability and validity of Quality of Life assessed by the Short-Form 36 and the Modular System for Quality of Life in patients with schizophrenia and patients with depression

Abstract

Reliability and validity of the Quality of Life (QoL) construct were investigated in healthy controls ( N=346), patients with depression ( N=114) and patients with schizophrenia ( N=91) using two different QoL instruments: the Short-Form 36 (SF-36), a well-established generic instrument measuring eight dimensions; and the Modular System for Quality of Life (MSQoL), a recently developed instrument measuring seven core dimensions and four specific modules (objective data, partnership, family, occupation). The MSQoL and the SF-36 were administered at three intervals (hospital admission, discharge and 4-month follow-up). Reliability, group profiles (clinical specificity), responsiveness, discriminant validity (with regard to sociodemographic, psychopathological, clinical and state variables) and convergent validity were tested. At admission, patients with depression had the lowest QoL level, patients with schizophrenia had an intermediate level, and controls had the highest QoL level. At discharge and follow-up, the two patient groups did not differ from each other, but still had lower levels than controls. Both patient groups improved significantly in QoL from admission to discharge. This improvement was confounded by improvement in depressive symptoms, but not in positive or negative symptoms. Current mood state influenced QoL assessments in all three samples substantially. In conclusion, QoL can be measured reliably and with sufficient responsiveness by the MSQoL and the SF-36 in psychiatric and non-clinical populations, although discriminant validity with regard to depression and current mood is questionable.