International Phase IV Field Study for the Reliability and Validity of the European Organisation for Research and...

The aim of this study was to validate the new European Organisation for Research and Treatment of Cancer Quality of Life Thyroid Cancer Module (EORTC QLQ-THY34). We enrolled 437 thyroid cancer patients from 17 countries. One group (n = 303), undergoing treatment or best supportive care, completed the questionnaires at three time points (before therapy [t1], 6 weeks later [t2], and 6 months after t2 [t3]). A second group (survivors ≥2 years after diagnosis, n = 134) completed it at a random baseline time point and a second time 1 week later. We determined internal consistency (using Cronbach's alpha), the scale structure (with confirmatory factor analysis), and discriminant validity (using known-group comparisons). Group 1 data were used to assess responsiveness and group 2 data to determine test-retest reliability using intra-class correlations (ICC). All 34 items fulfilled the criteria to be kept in the questionnaire. Cronbach's alpha was >0.70 in 8 of the 9 multi-item scales. All standardized factor loadings exceeded 0.40, confirming the proposed scale structure. The ICC was >0.70 in all scales expressing good test-retest reliability. Differences in scale scores between patients with different histology were >5 points in all scales. In all but one of the pre-specified scales (Dry Mouth), changes over time were ≥|4| points between at least two time points. The EORTC QLQ-THY34 with its 9 multi-item and 8 single-item scales is a reliable and valid tool to measure quality of life in thyroid cancer patients and can be used in future trials and studies.