Summarizing the fifteen scales of the EORTC QLQ-C30 questionnaire by five aggregate scales with two underlying dimensions: a literature review and an empirical study.

The intercorrelations among the 15 scales of the 30-item Core version of the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire suggest that one may combine (1) the physical functioning and role functioning scales, (2) the emotional functioning and cognitive functioning scales, and (3) the nine symptom scales. Together with the global health/quality of life scale and the social functioning scale, five measures remain. Principal component analysis of those five measures, using data from Japanese and Dutch breast and lung cancer patients, yielded two dimensions: (1) generalized health related quality of life and (2) health-independent psychological well-being. The correlations of these dimensions with the Brief Illness Perception Questionnaire and Karnofsky performance substantiated this interpretation.