Factor analysis of the psychosocial items of the EORTC QLQ-C30 in metastatic breast cancer patients participating in a psychosocial intervention study

The underlying factor structure of a subset of 12 items, which comprise the psychosocial subscales of the EORTC QLQ-C30 was explored in a group of wom en, all with metastatic breast cancer who were participating in a psychosoc ial intervention study. Two main factors were identified in this explorator y factor analysis, representing "emotional distress'' and "functional abili ty'' dimensions. A preliminary assessment of the external validity of the t wo factor structure was undertaken. The results support the validity of a s ummative "emotional distress'' and "functional ability'' score in this samp le of patients. The "functional ability'' score discriminated well for subg roups defined by clinical status indicators (e.g., performance status, pain , chemotherapy treatment, fatigue). The "emotional distress'' subscale disc riminated with respect to suffering, fatigue and sleep disturbance. Both su bscales converged with related concepts measured by independent instruments , providing support for convergent validity. Summative index scores may be advantageous for application in particular research situations; applying qu ality adjustments in health policy analyses; for screening purposes; to mon itor populations and make comparisons across broad groups and as stratifica tion variables in clinical trials. Further research to confirm the 2 factor structure is required in other samples before the interpretation can be ac cepted with confidence.