Objectives: Without clear guidelines, clinicians and health care providers are often uncertain how to interpret (quality of life) QOL scores. To facilitate the interpretation, QOL scores of multiple myeloma patients at diagnosis were compared with the scores of a reference population, and the clinical significance of QOL score differences and of changes in scores over time was assessed.
Methods: Data from two prospective Nordic Myeloma Study Group trials (221 patients <60 yr treated with high dose chemotherapy, and 203 patients >60 yr treated with melphalan and prednisone) were analysed. The EORTC QLQ-C30 questionnaire was used. The results were compared with the scores of an age- and gender-adjusted Norwegian reference population (n = 3000), using a regressional approach. The magnitude of the observed differences and of score changes during follow-up was estimated as effect size [score difference (SD)] and according to a subjective rating system as small, moderate or large.
Results: At diagnosis, the most distressing problems were pain and fatigue, reduced physical functioning, limitations in role functioning and reduced overall QOL. These differences from the reference population were statistically significant (P < 0.001), and large or moderate according to the rating systems. After the start of treatment, small to moderate improvement in mean QOL scores were observed for most domains.
Conclusion: Comparison with a reference population eases the interpretation of QOL scores and prevents overestimation of symptoms and underestimation of subjective treatment response. The agreement between the two methods to evaluate the meaning of differences and changes in QOL scores was good.