To optimise measurement precision, relevance to patients and flexibility, patient-reported outcome measures should ideally be adapted to the individual patient/study while retaining direct comparability of scores across patients/studies. This is achievable using item banks and computerised adaptive tests (CATs).
The aim of this project was to develop CAT versions of the 14 functional and symptom domains of the widely used health related quality of life questionnaire the EORTC QLQ-C30.
The general strategy for developing item banks for CAT measurement consisted of four phases: literature search to identify potential candidate items; formulation of new items compatible with the EORTC QLQ-C30 item style; expert evaluations and patient interviews; field testing and psychometric analyses, including factor analysis, item response theory calibration and simulation of measurement properties.
Based on more than 400 interviews and approximately 10,000 questionnaire responses from cancer patients recruited from 12 countries, the four phases of development resulted in a total of 260 unique items across the 14 domains. Each item bank consists of 7 to 34 items. The performance of the CAT instrument was validated in 700 cancer patients recruited across seven European countries.
This validation confirmed that the EORTC CAT Core measures the same domains as the EORTC QLQ-C30 with reduced floor and ceiling effects and generally with higher measurement precision allowing for the use of smaller samples (about 30% smaller on average) without loss of power compared to the EORTCQLQ-C30.
For further information about the EORTC CAT Core and if interested in using it, please visit https://qol.eortc.org/cat/