Psychometric validations and comparisons of schizophrenia-specific health-related quality of life measures
Introduction
Schizophrenia is characterized by early episodes and multidimensional symptoms that can be effectively monitored using measures of health-related quality of life (HRQoL), also a multidimensional construct. Because the Quality of Life Questionnaire in Schizophrenia (S-QoL) compares favorably to other disease-specific and generic HRQoL instruments (Bobes et al., 2005, Reine et al., 2005), it is recommended for assessing HRQoL in patients with schizophrenia (Reine et al., 2005).
The S-QoL is a self-report measure of disease-specific HRQoL developed for disease of schizophrenia (Auquier et al., 2003). The ratings of the S-QoL assess the current status of HRQoL levels. The S-QoL has 41 items rated on a five-point Likert-type scale, encompassing eight subscales. The total score is the index score, represented by the mean of the eight subscale scores, transformed to a scale of 0–100. The S-QoL has sound psychometrics and unidimensionality within each of the eight subscales (Auquier et al., 2003).
To enhance feasibility, Boyer et al. shortened the S-QoL to 18 items (Boyer et al., 2010). The item reduction has been validated by both classical test theory and item response theory. As a result, the S-QoL-18 still includes the same eight subscales but retains only 18 items, which is less than the half of the original number of items. The reduced number of items requires less time and facilitates administration. The S-QoL-18 has a high degree of comparability with the original S-QoL (Boyer et al., 2010). Therefore, the brief S-QoL-18 is currently suggested for use. The original S-QoL has been cross-culturally translated into Chinese (S-QoL-C) and is psychometrically valid (Chou et al., 2011).
This study aimed to validate a Chinese (Taiwanese) version of the S-QoL-18 (S-QoL-18-C) and to compare the S-QoL-18-C to other disease-specific HRQoL instruments, including another schizophrenia-specific measure: the Schizophrenia Quality of Life Scale–Revision 4 (SQLS-R4) Chinese version (Kuo et al., 2007, Wilkinson et al., 2000). Similar to the S-QoL-18-C, the SQLS-R4 can be completed within 5–10 min. To compare the S-QoL-18-C, SQLS-R4, and S-QoL-C (41 items) (Chou et al., 2011), subjects from an earlier study of the S-QoL-C, having the same sociodemographic characteristics, were employed (Chou et al., 2011). Of note, the psychometrics of these three instruments have not been compared simultaneously before. Furthermore, the S-QoL-18-C was compared with international reports of the S-QoL-18 (Auquier et al., 2013, Boyer et al., 2010), with the hypothesis that the S-QoL-18-C would show better psychometric properties than the others would. These findings can help guide researchers and clinical practitioners in selecting instruments for monitoring HRQoL levels in patients with schizophrenia. This study was conducted in Taiwan, where all citizens receive needed health care, including psychiatry services, through the National Health Insurance administration.
Section snippets
Subjects
The sample was taken from a former project (Chou et al., 2011) in which 41 patients were recruited to examine the reliability and convergent validity of the measure. Recruitment was by convenience sampling in a community hospital in central Taiwan, and subjects completed the baseline test and post-test within a 2-week interval. The inclusion criteria were as follows: (1) diagnosis of schizophrenia based on DSM-IV (1994) criteria, (2) age 18–65 years, (3) sufficient reading or listening
Results
The sociodemographic and clinical informations for the 41 subjects and three groups are briefly presented in Table 1, Table 2. Table 3 shows that there were no significant differences in the sociodemographics and HRQoL scores of the 30 healthy individuals compared with the WHOQoL-BREF norms for the same county. The ceiling and floor effects of the S-QoL-C-18 subscales were all less than 20% (Table 4), except for the psychological and self-esteem subscales. The index score and four subscales
Discussion
The purpose of this study was to validate the S-QoL-18-C and to compare its psychometric properties with those of the SQLS-R4 and the S-QoL-C (41 items) using the same research participants from earlier studies (Chou et al., 2011). These research participants also had sociodemographic characteristics similar to those of the participants in a S-QoL-18 validation study (Boyer et al., 2010), including gender ratio, mean age, and symptom severity. Most patients were single and had senior high
Conflict of interest
There is no conflict of interest.
Acknowledgments
We thank Drs. Boyer, L.; Wild, D.; Yao, G.; Hwu, H.G.; Lee, M.B.; and Wu, C.H. for permission to use the S-QoL-18, SQLS-R4, WHOQoL-BREF, PANSS, BSRS-5, and RSES for the validation of the S-QoL-18-C. Special appreciation is given to the raters of the PANSS, administrators of other measures, and all participants for their participation.
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