Validity and Reliability of the Persian Version of the “Quality of Life Scale” in Schizophrenia

Background: There are still controversies around the most accurate way to assess the quality of life in patients with schizophrenia. The “quality of life scale” (QLS) was designed to assess the quality of life of non-hospitalized patients with schizophrenia, regardless of their florid psychotic symptoms. Objectives: To validate the Persian version of the “quality of life scale” (QLS) in assessing the quality of life of patients with schizophrenia. Methods: Clinically stable outpatients with schizophrenia referred to Roozbeh hospital, Tehran University of Medical Sciences, as well as 75 healthy participants from September 2016 to March 2017 were enrolled. The QLS was translated following the WHO guidance. To evaluate the face and content validity, a group of experts were gathered to examine the conceptual structure, translation, and back-translation. To evaluate the convergent and discriminant validity, the world health organization quality of lifebref (WHOQOL-BREF), and the global assessment of functioning (GAF) were administered to 85 patients with schizophrenia and 75 healthy controls. To evaluate inter-rater reliability, two independent raters simultaneously assessed 52 patients. Results: Content validity index regarding relevance and clarity were 0.91 and 0.97, respectively. The discriminant validity assessment comparing the scores of the patients and the control group showed significant differences in all domains. The QLS scores had a positive correlation with GAF scores. No significant correlation was observed between the QLS and the WHOQOL-BREF domain scores among patients. Across different categories, Cronbach’s alphas were 0.90 for the interpersonal relations, 0.43 for the instrumental role, 0.95 for intrapsychic foundations, and 0.86 for the common objects and activities. The intra-class correlation (ICC) coefficients were more than 0.98 within all four domains. Conclusions: The Persian version of the QLS possesses desirable validity and reliability indices. The scale seems to measure diseasespecific aspects of quality of life when compared with more generic and self-rating instruments such as the WHOQOL-BREF.