Testing the EORTC Quality of Life Questionnaire on cancer patients with heterogeneous diagnoses.

This study aimed to contribute to the validation of the 30-item Quality of Life Questionnaire developed by the European Organization for Research and Treatment of Cancer Study Group (EORTC QLQ-C30). The sample consisted of 177 cancer patients with heterogeneous diagnoses. A series of scales representing various dimensions of quality of life were tested, including those proposed by the EORTC Study Group. Mokken's non-parametric latent trait model for unidimensional scaling was used as the basic scaling procedure. This model gives coefficients of scalability in addition to reliability coefficients. In terms of scalability measured by Loevinger's H, all EORTC Study Group scales, except the cognitive functioning scale were found to be quite satisfactory. The cognitive functioning scale and the role functioning scale were below the satisfactory level in terms of reliability (internal consistency). In total, our study strengthens the external validity of the EORTC QLQ-C30 and confirms that it may be used on cancer patients with various diagnoses.