Further evaluation of the EORTC QLQ-C30 psychometric properties in a large Brazilian cancer patient cohort as a function of their educational status.

Purpose: The European Organization for Research and Treatment of Cancer Core Quality of Life Questionnaire (EORTC QLQ-C30) is considered a valid instrument for use in Brazil. However, the previous Brazilian validation study included only 30 lung cancer patients and only measured test-retest reliability. The aim of this study was to evaluate the psychometric properties of the EORTC QLQ-C30 in a sample of cancer patients at different educational levels who completed the instrument administered by an interviewer.

Methods: Data from six prospective studies conducted by the same group of researchers were combined in this study (N = 986).

Results: Reliability was assessed using Cronbach's alpha coefficient, all values of which were >0.7, with the exception of cognitive functioning, social functioning, and nausea and vomiting (α = 0.57, α = 0.69, and α = 0.68, respectively). In multi-trait scaling analysis, convergent and divergent validity were considered adequate (validity indices were 91.6 and 97.4%). In general, moderate to strong correlations were found between the subscales of the EORTC QLQ-C30 and its respective dimensions from the WHOQOL-bref, the hospital anxiety and depression scale, and the Edmonton Symptom Assessment System (ESAS) instruments. In addition, the EORTC QLQ-C30 was able to differentiate groups of patients with distinct performance statuses and types of treatment (known-group validation). Statistical analyses were also performed on educational status, yielding similar results.

Conclusions: Detailed psychometric property data using the EORTC QLQ-C30 in Brazil are added by this study. In addition, we demonstrated that this instrument is in general reliable and valid regardless of the patient educational level.