Validation and reliability of the Dutch version of the EORTC QLQ-NMIBC24 Questionnaire Module for patients with non-muscle-invasive bladder cancer

BACKGROUND: The European Organisation for Research and Treatment of Cancer (EORTC) quality of life questionnaire for non-muscle invasive bladder cancer (QLQ-NMIBC24) has been available and applied for some years now, but has yet to undergo a full comprehensive psychometric evaluation. The aim of this study was to investigate the psychometric properties of the Dutch version of the EORTC QLQ-NMIBC24 questionnaire in patients with low, intermediate and high risk NMIBC. METHODS: We included patients newly diagnosed with NMIBC participating in the multicenter, population-based prospective cohort studies UroLife or BlaZIB. Psychometric evaluation included examination of the structural validity, reliability (i.e. internal consistency and test-retest reliability), construct validity (i.e. divergent validity and known-groups validity), responsiveness and interpretability. RESULTS: A total of 1463 patients who completed the baseline questionnaire of UroLife (n = 541, response rate 50%) or BlaZIB (n = 922, response rate 58%) were included. The percentage of missing responses were low for all non-sex related scales (< 1%) and ranged between 6.9% to 50.0% for sex-related scales. More than 15% of the patients obtained the lowest possible scores on nearly each scale (floor effect). The structural validity was adequate; the confirmatory factor analysis showed satisfactory results and all items of multiple items scales had higher within- than between-scale correlations. Reliability of the questionnaire was adequate for most multiple item scales (Cronbach's α ≥ 0.70 and intraclass correlation coefficient ≥ 0.70), with exception of the scales 'malaise' and 'bloating and flatulence'. The questionnaire also showed good construct validity; it showed low correlations with the items of the EORTC core questionnaire and was able to measure differences between risk-based subgroups. The responsiveness of the questionnaire was good, but the interpretability, i.e. minimal important change, could not be determined. CONCLUSIONS: This study shows that the measurement properties of the EORTC QLQL-NMIBC24 are good; it has a good structural validity, reliability (i.e. internal consistency and test-retest reliability), construct validity (i.e. divergent validity and known-group validity), and responsiveness. Interpretability could not be assessed. This questionnaire can be used to measure and monitor health-related quality of life of patients with NMIBC