DISEASE-SPECIFIC QUALITY-OF-LIFE - IS IT ONE CONSTRUCT

The objective of this study was to examine the structure of disease-sp ecific quality of life (QoL). Models of QoL with either one overall co nstruct or more constructs were tested and the relationships (factor l oadings) between the constructs and dimensions were established, using structural equation modelling. The models were tested over time to as sess the stability of the structure. To generalize the results further , disease-specific questionnaires of two very different chronic diseas es have been compared: inflammatory bowel disease (IBD) and Parkinson' s disease (PD). Questionnaires were mailed in 1994 and a repeated meas urement was conducted in 1995. Data were obtained from 222 IBD patient s and 235 PD patients. The results show that for both diseases, diseas e-specific QoL can be considered as one construct. The stability over time of the structure of the QoL models was satisfactory. In PD the fa ctor loadings between the dimensions and QoL were within a small range and remained the same over time, while in IBD, the factor loadings ha d a larger range and fluctuated more. These results imply that one mea ningful sum score can be obtained from these questionnaires.