Understanding the reliability and validity of the EORTC QLQ-C30 in Turkish cancer patients.

Quality of life (QOL) has become an important area to address. The most commonly used QOL tool in oncology is the European Organization for Research and Treatment of Cancer QOL measure (EORTC QLQ-C30). The aim of this study is to examine the reliability and validity of this widely used questionnaire in Turkish language. A total of 114 cancer patients were recruited in this study. The internal consistency of the subscales, concurrent validity between EORTC QLQ-C30 version 3.0 and Short Form-36 (SF-36), the correlations between the subscales of EORTC QLQ-C30 and Hospital Anxiety and Depression scale-Anxiety (HADS-A), and Hospital Anxiety and Depression scale-Depression (HADS-D) were also evaluated. Cronbach's alpha-coefficient for multi-item scales ranged from 0.56 to 0.85, with emotional functioning having the highest Cronbach's alpha-coefficient. General health/QOL subscale was correlated significantly with all other subscales. Modest correlations were found between relevant subscales of SF-36 and EORTC QLQ-C30 scales indicating good convergent validity. Although score of emotional functioning subscale was significantly correlated with HADS-A, no correlation was found with HADS-D. The correlations between general health/QOL and HADS-A and HADS-D were significant though Pearson's coefficients were below 0.4. The EORTC QLQ-C30 version 3.0 is a reliable and valid instrument and suitable for measuring the QOL in cancer patients in Turkey.