Instrumental activities of daily living in neuro-oncology: International validation of the EORTC IADL-BN32 questionnaire.

Neurocognitive impairments are common in patients with a brain tumour, and may negatively impact on functioning in daily life, particularly on instrumental activities of daily living (IADL). The EORTC IADL-BN32 questionnaire was developed to measure IADL in this patient population. In this international validation study, we evaluated the EORTC IADL-BN32 questionnaire on several psychometric properties in a large sample of patients with a primary or metastatic brain tumour. We administered the 32-item questionnaire three times: at 'baseline', after 2 weeks and after 3 months. Procedures were in accordance with EORTC Quality of Life Group module development guidelines. In total, 326 patients participated in the study. A bifactor scale structure showed satisfactory model fit measures, with five multi-item scales and two single items, and an IADL sum score. The internal consistency of the multi-item scales ranged from good to excellent (range Cronbach's α: 0.86-0.97). We found significant differences in scale scores between patients with and without neurocognitive impairments or complaints, supporting the construct validity. Initial cross-cultural validity analyses showed indications of item response biases for certain items. Analyses indicated moderate to good test-retest agreement (intraclass correlation coefficient > 0.70) between baseline and the 2-week follow-up assessment for all but one scale. Deterioration of EORTC IADL-BN32 scale scores were consistent with clinically relevant deterioration on other functional measures with small to large effect sizes, however, subgroup sample sizes were small. Overall, the EORTC IADL-BN32 questionnaire exhibited adequate to excellent psychometric properties. Cross-cultural validity and responsiveness should be further explored.

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Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.