Factorial invariance of the WHOQOL-BREF among disease groups.

To compare health-related quality of life (QOL) across groups, researchers have to assure that items of a QOL measure represent the same constructs across groups. This study investigated factorial invariance of the WHOQOL-BREF between a healthy population and populations with diseases using the data from the 2001 National Health Interview Survey (NHIS) in Taiwan. The NHIS was conducted by stratified multistage systematic sampling resulting in responses from 13,010 participants aged 20 approximately 65 who completed the WHOQOL-BREF. The analysis was limited to 5 diseases where at least 200 individuals had that specific single condition; these were pulmonary disease, hypertension, peptic ulcer, sinusitis and liver disease. In this study, confirmatory factor analyses (CFA) on a four-factor model were conducted. Two-group analyses with unconstrained/constrained parameters were conducted to confirm the comparability of CFA factor structures between groups. Generally, the xi(2) discrepancy tests showed that different disease groups and their matched healthy groups shared the same first- and second-order factor loadings. Moreover, different disease groups shared the same first- and second-order factor loadings as well. In other words, after controlling age and gender, same perceptions on the WHOQOL-BREF questionnaire were found between disease and matched healthy groups and across disease groups.