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

Abstract

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