ABSTRACT
Aims: Health-related quality of life (HRQoL) of Type 2 diabetes mellitus (T2DM) is a growing concern globally given the increase in T2DM prevalence. Generic HRQoL instruments are important to allow cross-cultural, cross-population and cross-study comparisons. The short version of the World Health Organization Quality of Life (WHOQOL-BREF) questionnaire is a widely used generic questionnaire. Hence, we aimed to evaluate the psychometric properties of the WHOQOL-BREF among patients with T2DM in Singapore. Study Design: Patients at a diabetes outpatient specialist clinic in Singapore were recruited via convenience sampling. Classical Test Theory methods were used to evaluate data quality, scaling assumptions, targeting, internal consistency reliability and construct validity (structural, convergent and discriminant) and criterion validity using HbA1c control (good versus poor). Principal Component Analyses (PCA) and Confirmatory Factory Analyses (CFA) were performed to assess unidimensionality (domain-level) as well as conformity with the original four-factor structure. Exploratory Factor Analysis (EFA) was done if CFA indicated lack of fit. Results: 212 subjects were analyzed of whom 50% were Chinese, 28% Indians, 11% Malays and 10% others. 63% were males with mean (SD) age 45.8 (11.9) years. Data quality was superior, scaling assumptions were met, targeting was satisfactory and internal consistency was achieved. PCAs were compatible with unidimensionality, except in the Physical domain. Domain level CFA indicated that unidimensionality had poor fit and overall CFA did not support the original 4-factor structure. EFA runs showed that the Physical and Environment domains overlapped while the Social and Psychological domains could not be recovered. Therefore construct (structural) validity was not established. Criterion validity was not achieved as all domains could not discriminate between those with good versus poor HbA1c control. Conclusion: Construct and criterion validity of WHOQOL-BREF posed some concerns. Thus, we recommend that an adequately-powered random sample of T2DM patients in Singapore be studied to confirm the findings of our study.