Psychometric evaluation of the Short Form 36 Health Survey (SF-36) and the World Health Organization Quality of Life Scale Brief Version (WHOQOL-BREF) for patients with schizophrenia

Abstract

Quality-of-life (QoL) instruments measure the overall health status of people with schizophrenia, for whom the activities of daily life are often difficult. However, information on the psychometric properties of scores from the Short Form 36 Health Survey (SF-36) and the World Health Organization Quality of Life Scale Brief Version (WHOQOL-BREF), 2 commonly used generic QoL instruments in this population, is limited. Thus, we used a multitrait-multimethod analysis plus confirmatory factor analysis (CFA) to examine their psychometric properties. To test the reliability of their scores, we used methods of absolute reliability (standard error of measurement [SEM] and smallest real difference [SRD]) and relative reliability (i.e., intraclass correlation coefficient [ICC]). We recruited 100 patients with schizophrenia from a psychiatric hospital in southern Taiwan. All participants filled out the SF-36 and the WHOQOL-BREF at baseline and 2 weeks later. The participants' QoL scores were lower than those of the Taiwan general population (ps < .01), and CFA indicated that the constructs of QoL scores for the SF-36 (comparative fit index [CFI] = .918; incremental fit index [IFI] = .919; Tucker-Lewis index [TLI] = .885) and the WHOQOL-BREF (CFI = .967; IFI = .967; TLI = .900) were acceptable. The SEM and SRD analyses suggested that the total scores of the SF-36 (SEM% = 10.03%; SRD% = 27.80%) and of the WHOQOL-BREF (SEM% = 5.55%; SRD% = 15.40%) were reliable. Also, our results demonstrated that the WHOQOL-BREF scores were more reliable and valid than the SF-36 scores for assessing people with schizophrenia. The scores of both questionnaires were valid and reliable and detected different aspects of QOL in the population with schizophrenia.