Do the SF-36 and WHOQOL-BREF Measure the Same Constructs? Evidence from the Taiwan Population* |
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| Authors: | I-Chan Huang Albert W Wu Constantine Frangakis |
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| Institution: | (1) Department of Health Policy and Management, Bloomberg School of Public Health, The Johns Hopkins University, Baltimore, MD, USA;(2) Department of Epidemiology, Bloomberg School of Public Health, The Johns Hopkins University, Baltimore, MD, USA;(3) Department of Medicine, School of Medicine, The Johns Hopkins University, Baltimore, MD, USA;(4) Department of Biostatistics, Bloomberg School of Public Health, The Johns Hopkins University, Baltimore, MD, USA;(5) Department of Health Policy and Management, Bloomberg School of Public Health, The Johns Hopkins University, 624 North Broadway, Baltimore, MD Md 21205-1901, USA |
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| Abstract: | Background: The SF-36 and WHOQOL-BREF are available for international use, but it is not clear if they measure the same constructs. We
compared the psychometric properties and factor structures of these two instruments. Methods: Data were collected from a national representative sample (n=11,440) in the 2001 Taiwan National Health Interview Survey,
which included Taiwan versions of the SF-36 and WHOQOL-BREF. We used Cronbach’s alpha coefficient to estimate scale reliability.
We conducted exploratory factor analysis to determine factor structure of the scales, and applied multitrait analysis to evaluate
convergent and discriminant validity. We used standardized effect size to compare known-groups validity for health-related
variables (including chronic conditions and health care utilization) and self-reported overall quality of life. Structural
equation modeling was used to analyze relationships among the two SF-36 component scales (PCS and MCS) and the four WHOQOL
subscales (physical, psychological, social relations, and environmental). Results: Cronbach’s alpha coefficients were acceptable (⩾0.7) for all subscales of both instruments. The factor analysis yielded two
unique factors: one for the 8 SF-36 subscales and a second for the 4 WHOQOL subscales. Pearson correlations were weak (<0.3)
among subscales of both instruments. Correlations for subscales hypothesized to measure similar constructs differed little
from those measuring heterogeneous subscales. Effect sizes suggested greater discrimination by the SF-36 for health status
and services utilization known groups, but greater discrimination by the WHOQOL for QOL-defined groups. Structural equation
modeling suggested that the SF-36 PCS and MCS were weakly associated with WHOQOL. Conclusions: In this Taiwan population sample, the SF-36 and WHOQOL-BREF appear to measure different constructs: the SF-36 measures health-related
QOL, while the WHOQOL-BREF measures global QOL. Clinicians and researchers should carefully define their research questions
related to patient-reported outcomes before selecting which instrument to use.
* Presented in part at (1) 11th Annual Conference of the International Society for Quality of Life Research. Hong Kong, China,
2004. (2) 2004 Quality of Life Symposium – Conceptualization and Measurement issues in QOL. Tai-Chuan, Taiwan, 2004 |
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| Keywords: | Health status Quality of life SF-36 WHOQOL-BREF |
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