Reference value data are historical data from the EORTC QLQ-C30 and/or its modules obtained in previous clinical studies, trials, or stored in registries. These data are from specific subgroups of patients with an oncological disease typically further stratified by age, sex, disease stage, and performance status, allowing a more accurate comparison. Reference data provide context to aid interpretation of EORTC PRO scores and can be used in the following scenarios:

  • Sample size calculation
    (Reference data can be used to build estimations of sample size requirements when planning a clinical trial with a primary or secondary PRO endpoint. Adequate sample size is necessary to provide sufficient power to test the significance of treatment effects.)
  • Comparisons of scores from groups of patients with similar characteristics
    (Reference data provide information about the distribution of QoL scores for given cancer populations with certain predefined characteristics, in particular stage and cancer site. This information can be used to explain unexpected differences in clinical outcomes, e.g. an unexpected response rate or median survival, to identify populations that need special attention and carry out comparisons among different countries.)
  • Familiarity with the distribution of scores for a scale
    (Knowledge about the distribution of QOL scores at baseline and the possible magnitude of change over time in a certain patient group is important to be considered at the design stage of a clinical trial. It can help in establishing realistic hypotheses and a priori defined cut-off points.)
  • Comparison of an individual patient’s score with patients with similar characteristics
    (Reference data provide clinicians with a comparison to evaluate if an individual patient’s responses are higher or lower than might be expected when looking at PRO data from patients with similar characteristics or his and her pre-treatment scores. However, there are no widely accepted standard thresholds for reference values to trigger clinical actions.)
  • Quality control in translation procedures
    (The EORTC Quality of Life Study Group has developed procedures for the translation of the EORTC QLQ-C30 and its cancer site-specific modules, available here. Comparison of data from new translations with available reference data from original language versions can be helpful to identify obvious discrepancies caused by incorrect translations.)

The EORTC QOL Group aims to provide a solid source of reference data for use in research and clinical practice. For this reason, there are current efforts to update the pool of EORTC QOL reference value data, develop a database and an associated online accessible user interface for reference value calculation. The previous version of the manual on EORTC QLQ-C30 Reference Values (Scott et al 2008) is available here.