In contrast to reference values that are obtained from cancer patients (see “What is reference data?”), normative data are obtained from the general population. Like with reference values, general population norm data enable the comparison of patient-reported outcomes (PRO) data collected in a specific context (e.g., clinical trial, routine monitoring) with a reference group, in this case, the general population of a specific country or the general populations of several countries combined. When comparing trial data (or routine data, etc.) to norm data, it can be established whether one’s data are in line with expectations and it can also be identified which of the EORTC QLQ-C30 scales show discrepancies that would be considered clinically meaningful (see “How do I interpret QoL scores?”).
General population norm data are often collected through a panel research company which is an efficient way of collecting a large amount of data that is representative of a country’s general population in terms of sex, age, region, hometown size, household size and socioeconomic status (note, as these panels typically run online, panel research companies usually claim that their internet panels are representative for only those of the general population that have internet access). Ideally, as with reference values, the comparison is undertaken within subgroups, e.g., a female patient, aged 54 years, is ideally compared to the female general population in age group 50-59 years rather than comparing her to an overall general population norm score.
Norm data for the EORTC quality of life questionnaires are currently available for the EORTC QLQ-C30 and the EORTC computer-adaptive test (CAT), the EORTC CAT Core. The European Norm for both EORTC instruments is based on 11 European countries (i.e., 10 countries of the European Union and the UK). National general population norm data are available for each of these 11 countries and also for Russia, Turkey, Canada and the US (see the two core papers Nolte et al., 2019, https://doi.org/10.1016/j.ejca.2018.11.024 and Liegl et al., 2019, https://doi.org/10.1016/j.ejca.2018.11.023). If you are interested in using EORTC QLQ-C30 norm data for your project (beyond those data that have already been published), these data are available upon request. Please use the following link: eortc.be/services/forms/erp/request.aspx, using EORTC study number 1519.
