The objective of this study was to test the reliability and validity of the Iranian Version of the European Organization for Research and Treatment of cancer (EORTC) Quality of life questionnaire (QLQ-C30) and it’s supplementary Breast Caner-Specific Quality of life Questionnair (QLQ_BR23). The English-language version of the questionnaires was translated into Persian (Iranian language) and their final forms were approved by the EORTC Study Group on Quality of life and then these were used in this study. The questionnaires were administered at two points in time to a consecutive sample of 168 newly diagnosed breast cancer patients and almost all of them (99%) found the questions easy to understand and acceptable. Cronbach’s alpha coefficient for multi-item scales (to test reliability of the core questionnaire) (QLQ-C30) ranged from 0.48 to 0.95 at baseline and from 0.52 to 0.98 at follow-up administration of the questionnaire. The Breast Cancer-Specific Quality of life Questionnaire (QLQ-BR23) showed similar results for multi-item scales ranging form 0.63 to 0.92 at baseline and from 0.75 to 0.92 at fallow-up administration of the questionnaire.
Validity analysis of Quality of life Questionnaire (QLQ-C30) was performed using inter-scale correlation. Almost all inter-scale correlations were statistically significant in the expected direction. Also, validity analysis of the two questionnaires was performed using know-groups Comparison. The results of this analysis showed that all functional and symptom scales discriminated between subgroups of patients differing in clinical status as defined by their performance status and disease stage. In addition, all functional and symptoms scales in Breast Cancer-Specific Quality of life Questionnaire (QLQ-BR23) detected change over time as a function of changes in patient’s performance status.
In general, the findings of this study indicated that Iranian version of the EORTC QLQ-C30 is a reliable and valid measure of quality of life in cancer patient. Also, the EORTC QLQ-BR23 is a reliable and valid supplementary measure of quality of life in breast cancer patients.
Both questionnaires can be used in clinical trials and studies of outcome research in oncology.