Development of computerised adaptive testing (CAT) for the EORTC QLQ-C30 dimensions: general approach and initial results for physical functioning

Background
Health-related quality of life (HRQOL) questionnaires should ideally be adapted to the individual patient and at the same time scores should be directly comparable across patients. This is achievable using a computerised adaptive test (CAT). Basing the CAT on an existing instrument enables measurement within an established HRQOL framework and allows backward-compatibility with studies using the original instrument. Because of these advantages the EORTC Quality of Life Group (QLG) has initiated a project to develop a CAT version of the widely used EORTC QLQ-C30.

Methods
We present the EORTC QLG’s strategy for developing a CAT. For each dimension of the EORTC QLQ-C30 our approach includes literature search and conceptualisation, formulation of new items, expert and patient evaluations, field-testing, and psychometric analyses of the items. The strategy is illustrated with the initial results of the development of CAT for physical functioning (PF).

Results
We identified 975 PF items in the literature. Of these, 407 items were deemed relevant, i.e. measured one of the PF aspects measured by the QLQ-C30. Based on these items we developed 86 new items. Review by the EORTC CAT-project group reduced this to 66 items. Based on expert and patient evaluations several items were revised and the list was further reduced to 51 items.

Conclusions
Based on the findings for PF, we believe that our approach will generate item pools that are relevant and appropriate for cancer patients. These will form the basis for a backward-compatible CAT assessing the HRQOL dimensions of the EORTC QLQ-C30.