The specificity of quality-of-life measures among the seriously ill

The need to address the impacts of serious disease and the effectiveness of interventions has led to the development of numerous measures of the quality of life. The research reported here explores the possibility that widely used measures do not truly distinguish among separate dimensions of the quality of life in a seriously ill population, but reflect a generalized tendency among such individuals to respond negatively to interviewers' questions about their well-being. This research examines three widely used measures--the Sickness Impact Profile (SIP), the Profile of Mood States (POMS), and the McGill Pain Questionnaire (MPQ)--as applied to 536 individuals with recent cancer diagnoses. In a multitrait-multimethod matrix, correlation coefficients among measures believed to reflect the same phenomena are consistently higher than correlation coefficients among measures supposed to reflect different phenomena. In a factor analysis performed on all 536 subjects, the unrotated factor matrix indicates that no single factor explains a preponderance of the variance in individual measures. Orthogonal rotation indicates that subscales from the SIP, POMS, and MPQ generally load on factors defined by the scales of which they are part. These findings were replicated on subsamples of subjects with particularly severe disease. The study suggests that the SIP, POMS, and MPQ measure the specific dimensions their names imply, even among individuals with illnesses posing immediate threats to survival.