RESUMO
The aim of this study was to assess construct validity and internal consistency reliability of the Greek EORTC QLQ-C30 and QLQ-BR23 instruments. A sample of female breast cancer patients (n= 105) were self-administered the QLQ-C30, QLQ-BR23 and SF-36 and questions on treatment and socio-demographic status. Hypothesised scale structure, reliability (Cronbach's α) and construct validity (convergent, discriminative, concurrent and known-groups) were assessed. Multitrait scaling confirmed scale structure of the QLQ-C30 and QLQ-BR23 with good item convergence (92% and 85%), and discrimination (87% and 84%) rates. Cronbach's α was >0.70 for all but one scale (cognitive functioning). Strength of Spearman's correlations between the QLQ-C30 and SF-36 scales assessing similar health-related quality of life dimensions ranged from 0.25 to 0.64 (P < 0.01). Construct validity was confirmed with satisfactory results for interscale correlations and known-groups comparisons. QLQ-BR23 scales showed comparatively low (<0.40) correlations with QLQ-C30 functional scales, and higher correlations with conceptually related symptom scales. Most QLQ-C30 and QLQ-BR23 scales discriminated between pre-treatment and current treatment patients. The overall psychometric results for the Greek version of the QLQ-C30 and QLQ-BR23 confirmed it as a reliable and valid questionnaire for assessing breast cancer-specific HRQoL in Greece.