Psychometric properties of the General Functioning Questionnaire (GFQ-58) used for screening for symptoms of psychopathology and overall level of functioning

Abstract

Aim. Measuring severity of psychopathological symptoms using self-assessment questionnaires is important for clinical and scientific research. However, there is no widely-available Polish tool which measures both overall functioning and severity of a broad spectrum of psychopathological symptoms. This paper describes the designing of such a tool - the General Functioning Questionnaire (GFQ-58). Methods. Three studies were conducted to verify the validity and reliability of the GFQ-58: (1) a study comparing 30 individuals diagnosed with schizophrenia and 30 with no psychiatric diagnosis; (2) a correlational study on 602 individuals exploring relationships between the GFQ-58 and tendency for rumination and quality of life; and (3) a study on 37 patients from a ward which treats neurotic and personality disorders, exploring the relationships between the GFQ-58 and tools for measuring severity of psychopathological symptoms, overall functioning and neurotic personality. Results. The first study revealed large differences between individuals suffering from schizophrenia and healthy individuals in the overall score of the questionnaire (p < 0.001; d = 1.30) and some of its subscales. The second study showed strong relations between the GFQ-58 and both severity of rumination (p < 0.001; ρ = 0.64) and quality of life (p < 0.001; ρ = - 0.81). The third study identified relationships between the GFQ-58 and tools measuring various psychopathological symptoms, overall functioning and neurotic personality. These relationships were moderate or strong (all p ≤ 0.001; r = 0.43-0.86). Reliability of the overall score was satisfactory in all studies (Cronbach's a = 0.89-0.92). Conclusions. The GFQ-58 has satisfactory validity and reliability. It can be used in both scientific and clinical research as a screening tool for measuring overall functioning and severity of psychopathological symptoms.