OBJECTIVE: To improve measurement precision, the European Organisation for Research and Treatment of Cancer (EORTC) Quality of Life Group is developing an item bank for computerized adaptive testing (CAT) of emotional functioning (EF). The item bank will be within the conceptual framework of the widely used EORTC Quality of Life questionnaire (QLQ-C30).

STUDY DESIGN AND SETTING: On the basis of literature search and evaluations by international samples of experts and cancer patients, 38 candidate items were developed. The psychometric properties of the items were evaluated in a large international sample of cancer patients. This included evaluations of dimensionality, item response theory (IRT) model fit, differential item functioning (DIF), and of measurement precision/statistical power.

RESULTS: Responses were obtained from 1,023 cancer patients from four countries. The evaluations showed that 24 items could be included in a unidimensional IRT model. DIF did not seem to have any significant impact on the estimation of EF. Evaluations indicated that the CAT measure may reduce sample size requirements by up to 50% compared to the QLQ-C30 EF scale without reducing power.

CONCLUSION: On the basis of thorough psychometric evaluations, we have established an EF item bank of 24 items. This will allow for more precise and flexible measurement of EF, while maintaining backward compatibility with the QLQ-C30 EF scale.