Interpreting quality of life data

Although the European Organization for Research and Treatment of Cancer (EORTC) core 30-item Quality of Life Questionnaire (QLQ-C30) is widely used in cancer patients, as with all health-related quality of life (QoL) instruments there are issues of interpretation. What does it mean if, on a scale from 0 to 100, a cancer patient reports a score of 50 for overall QoL? Is an improvement to 55 worthwhile? Various approaches have been used to aid interpretation [ 1 Fayers P. Machin D. Quality of Life Assessment, Analysis and Interpretation. J. Wiley & Sons, Chichester2000 Google Scholar ], and one method is to produce tables of ‘normative’ or ‘population-based reference values’, based upon the general population. Normative data (‘norms’) make it possible to compare the score of a patient against the average score within the population. Norms, being usually based upon a large random sample from a national population, also allow the impact of covariates such as age and gender to be explored. Since QoL scores vary markedly with both these factors, it will frequently be important to make allowance for them when interpreting the results from clinical trials or other studies, or when examining the scores for individual patients.