Psychometric properties of the General Functioning Questionnaire (GFQ-58) used for screening for symptoms of psychopathology and overall level of functioning
Rafał Styła, Joachim Kowalski
Abstract
OBJECTIVES: 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 describesthe 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; . = 0.64) and quality of life (p < 0.001; .=-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 . = 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.