A new approach to combining clinical relevance and statistical significance for evaluation of quality of life changes in the individual patient

Objective: Empirical investigation of formerly proposed criteria for relevant changes of health-related quality of life (QOL) regarding their use for monitoring changes in the individual patient. Suggestion of a new criterion trying to overcome the drawbacks of former criteria. Study Design and Setting: QOL data were collected longitudinally in 160 cancer patients receiving chemotherapy at an oncological outpatient unit, giving rise to a total of 975 QOL assessments. QOL was measured using the European Organization on Research and Treatment of Cancer Quality of Life Core Questionnaire. Several formerly suggested criteria of relevant change (distribution based, anchor based) were compared in terms of both prevalence and statistical significance of the resulting relevant changes. Results: When considering criteria of relevant change suggested in the literature, high proportions (average: 42.3-48.3%) of reputedly relevant changes were found. The majority of these changes (average: 55.8-62.2%) were statistically insignificant. Combination of an increased threshold for clinical relevance with the concept of statistical significance resulted in a more meaningful change criterion. Conclusion: Formerly recommended thresholds of relevant change in QOL appear to be unduly low when focusing on the individual patient. A modified criterion is therefore suggested for this case. However, more research is needed for validation and refinement of the proposed criterion. (C) 2010 Elsevier Inc. All rights reserved.