Confirmatory factor analysis of the quality of life scale and new proposed factor structure for the quality of life scale-revised
Introduction
The Quality of Life Scale (QLS) was developed over 30 years ago initially for the purpose of measuring the deficit syndrome (Heinrichs et al., 1984), a proposed subtype of schizophrenia characterized by persistent, primary negative symptoms (Carpenter et al., 1988, Kirkpatrick and Galderisi, 2008). The QLS is a semi-structured interview designed to assess four different areas of psychosocial adjustment, including Interpersonal Relations, Instrumental Role (e.g., work, school, homemaker), Intrapsychic Foundations (e.g., motivation, sense of purpose), and Common Objects and Activities (e.g., owning a watch, use of public transportation). Although the QLS was replaced by the Deficit Syndrome Scale as a measure of the deficit syndrome (Kimhy et al., 2006, Kirkpatrick et al., 1989), it has been widely used as a measure of psychosocial functioning in the intervening years since its publication (Bradley et al., 2006, Chou et al., 2012, Norman et al., 2000, Rabinowitz et al., 2012).
Numerous studies have supported the validity of the QLS as a measure of psychosocial functioning in schizophrenia and other severe mental illnesses (SMI) (Ascher-Svanum et al., 2013, Bellack et al., 1990, Faries et al., 2012, Thwin et al., 2013). Given the lack of a “gold standard” measure of psychosocial functioning in schizophrenia, the QLS has often been used in treatment studies. The QLS has enjoyed particularly widespread use in research on the treatment of prodromal psychosis states (Kim et al., 2013, McFarlane et al., 2012) and people recovering from a first episode of psychosis (Baksheev et al., 2012, Grootens et al., 2011, McEvoy et al., 2007, Perkins et al., 2004, Robinson et al., 2010). Despite the popularity of the QLS as an outcome measure in schizophrenia research, the factor structure of the QLS has not been empirically evaluated. Examination of the underlying factor structure of an instrument can improve the precision of the measurement of the central domains, as well as lead to refinements in the instrument that further increase its validity and sensitivity to change. This article describes the evaluation of the factor structure of the QLS based on several study samples of people with schizophrenia-spectrum disorders and other severe mental illnesses.
Section snippets
Methods
The analyses were based on data from four de-identified treatment studies of people with schizophrenia and other severe mental illnesses. All of the studies received IRB approval from their corresponding institutions. For the purposes of the present study, two datasets were formed, in order to have a sufficient sample size to conduct confirmatory factor analysis, one based on three studies conducted at the Dartmouth Psychiatric Research Center and Center for Psychiatric Rehabilitation (Dataset
Results
Item #12 (Work Satisfaction) was discarded in the analysis because it is rated as “not relevant” for individuals who are not working and most study participants (over than 70%) were unemployed. The means and standard deviations for the remaining 20 QLS items for Dataset #1, Times 1, 2, 3, and 4, and Dataset #2, organized according to the four factor model proposed by Heinrichs et al. (1984) are shown in Table 2.
Discussion
The original four-factor structure for the QLS (Heinrichs et al., 1984), including Interpersonal Relations, Instrumental Role, Intrapsychic Foundations, and Common Objects and Activities, was evaluated with a confirmatory factor analysis (CFA) and found to be a poor fit for Dataset #1. However, subsequent exploratory factor analyses (EFAs) with the same dataset led to the identification of a more parsimonious three factor solution based on 16 of the original 21 QLS items (the QLS-Revised:
Conflict of interest
None of the authors have any conflicts of interest to report.
Contributors
Kim T. Mueser, Min Kim, Jean Addington, Susan R. McGurk, Sarah I. Pratt, and Donald E. Addington.
Role of the funding source
The funding sources for this research (NIMH, NIDILRR) had no role in the production of this study, including either the data analysis or review of the manuscript.
Acknowledgement
This research was supported by NIMH grants #K23 MH080021 and #R01 MH077210, and NIDILRR grant (#90AR5018) for Advanced Research Training Program in Employment and Vocational Rehabilitation of Persons with Psychiatric Disabilities.
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