Quality of Life Group (QLG)

The Quality of Life Group (QLG) was created within the European Organisation for Research and Treatment of Cancer (EORTC) to advise the EORTC Headquarters and various cooperative groups on the design, implementation and analysis of Quality of Life (QOL) studies within selected Phase III clinical trials.

From its inception, the QLG has included a broad range of professionals, including oncologists, radiotherapists, surgeons, psychiatrists, palliative care specialists, psychologists, social workers and research methodologists. Within this broad cultural mix of both professional background and language and geography, a number of research projects have been and are still being undertaken, including the development of the QLQ-C30 and disease specific modules. More information on the history, aims, activities and projects of the group can be found in the respective links.


Quality of Life Department (QLD)

The Quality of Life Department (QLD) was established at the EORTC Headquarters in 1993 and has since been involved in all EORTC QOL activities. The QLD provides support for the evaluation of quality of life in EORTC cancer clinical trials, supports the QLG and is involved in QOL research activities. The main activities of the QLD are described here.


Construct or latent variable

In psychometric research, the latent variable is the underlying construct or phenomenon which the instrument intends to measure (e.g. quality of life, anxiety, coping). Usually, this cannot be quantified directly, but it is presumed that the latent variable takes on specific values under some specified set of conditions.




An item is a question whose answer is the manifestation of an underlying variable or construct. Several items reflecting one construct are often used to increase reliability. They then constitute a scale.




Scales are measurement instruments, which are a collection of items. They are intended to reveal levels of underlying variables, which are not readily observable by direct means.

A questionnaire can consist of several scales and items. The QLQ-C30 for example includes five functional scales (physical, role, emotional, cognitive and social), three symptom scales (fatigue, nausea & vomiting and pain) and a global health status/QOL scale. Furthermore, it contains six single items (dyspnoea, insomnia, appetite loss, constipation, diarrhea and financial difficulties).




Validity is a psychometric property of a measure, which implies that the measure detects what it is designed to detect. There are different forms of validity, most importantly:

Content validity: This is concerned with whether the items used in the questionnaire appear sensible and likely to measure the domain or construct of interest. It looks at whether the items in the tool appear to cover all aspects of the domain, and if they are relevant to the problem.

Construct validity: When constructing an instrument it may be hypothesized that a collection of domains/issues will measure the construct under investigation. Construct validity looks at the theoretical relationships between the domains and the extent to which the measure might actually be measuring the construct it is supposed to. Techniques to look at construct validity include comparing results with established existing measures of the same construct and 'known group' comparisons where the instrument is used in different patient groups (e.g. early v. advanced disease or good performance status v. poor performance status) and seeing how results compare with those predicted. A broad range of analyses are available to evaluate the validity and responsiveness of the questionnaire scales and single items. This topic is discussed extensively in Guidelines for module development.




Reliability is the psychometric feature of a questionnaire, which refers to the extent to which the tool will yield the same outcome in repeated use in the same population. This is usually checked by the test-retest method where patients complete an instrument once and then again a few days later. The time interval is usually sufficiently short that it is unlikely that the construct being measured will have changed significantly, but sufficiently long that patient recall will not bias their second response.

Reliability is also used in another context to check that all the items within a scale are consistent and appear to be measuring the same construct. A number of statistical techniques can be used to check for 'internal consistency' within a scale. For example the three questions: 'Did you need to rest?' 'Have you felt weak?' 'Were you tired?' from the QLQ-C30 all appear to be measuring fatigue, whilst the question 'Have you had trouble sleeping?' is a single item measuring only sleep.




The EORTC quality of life questionnaire (QLQ) is an integrated system for assessing the health-related quality of life of cancer patients participating in international clinical trials. The EORTC has adopted a modular approach to QOL assessment, consisting of a core questionnaire(EORTC QLQ-C30) to be administered, if necessary with a module specific to tumour site, treatment modality or a QOL dimension.

The QLQ-C30 is the product of more than a decade of collaborative research. It is a questionnaire for patient self-completion, composed of multi-item and single scales. These include five functional scales (physical, role, emotional, social and cognitive), three symptom scales (fatigue, nausea & vomiting and pain) and a global health status/QOL scale and six single items (dyspnoea, insomnia, appetite loss, constipation, diarrhea and financial difficulties).



A module is defined as a set of items assessing QOL issues not (sufficiently) covered by the core questionnaire and considered to be relevant for the target population and the research question. This set of items may refer to disease symptoms related to the tumour site or stage within the tumour site, side effects and other issues related to treatment, or additional QOL dimensions that are relevant across diagnoses and treatment modalities. Modules should always be used in addition to the core questionnaire.

Within the QLG, new modules are developed according to set Guidelines, before becoming available for use as  validated modules.


Item Bank


The Item Bank is a database which includes all items from the EORTC QLQ-C30 and all existing EORTC modules in all available languages. It is accessible through the Internet after request of a user name and password from the Item Bank database administrator. Please contact Dagmara Kulis . Researchers who want to use the EORTC QLQ-C30 or EORTC modules, should NOT register to use the Item Bank, but fill in a user's agreement by clicking here.

On the other hand, the main aims of the Item Bank are:

  • to improve the quality of modules and standardize the wording of items of existing and future modules;
  • to improve the speed and quality of module development;
  • to improve the speed of translations;
  • to permit the selection of a limited number of trial-specific items in conjunction with existing modules.

More opportunities for using and further developing the item bank to broaden its applications are currently being studied within the QLG. More details on the use and development of the Item Bank can be found here.




The EORTC QLQ-C30 and some disease specific modules are presently translated into several different languages. This is done according to strict guidelines (see Manuals). Briefly, the process involves two forward translations (from English into language X) and two backward translations (from language X into English). A coordinator (a native speaker of language X) is appointed to ensure that the procedure is adhered to, and to also make a final judgement, when necessary, if translations should differ.

More information on availability of translations can be found on the relevant questionnaire page, information on getting translations done can be obtained from the Translation Team Leader .