The comparability of quality of life scores. a multitrait multimethod analysis of the EORTC QLQ-C30, SF-36 and FLIC questionnaires.

This study investigates whether similarly named subscales of three quality of life questionnaires, the European Organization for Research and Treatment of Cancer Quality of Life Core Questionnaire (EORTC QLQ-C30), the Medical Outcome Study Quality of Life Questionnaire Short Form 36 (SF-36) and the Functional Living Index Cancer questionnaire (FLIC) assess similar aspects of the patients' quality of life. A multitrait multimethod analysis on the answers of 234 cancer patients showed that subscale correlations as indicators of convergent validity significantly exceed corresponding correlations of discriminant validity in five of the seven dimensions analysed (physical functioning, emotional functioning, pain, fatigue/vitality and nausea/vomiting). The results of the social functioning and overall health subscales are less clear. Content analysis of the social functioning scales reveals that this domain is differently operationalised in the three questionnaires. Linear regressions of the overall health subscales suggest that patients interpret overall health questions of the three questionnaires differently. The results show that overall health subscales of these three questionnaires cannot be equated, while most specific subscales provide valid results.