Psychometric testing of fatigue instruments for use with cancer patients.
BACKGROUND: Cancer treatment-related fatigue (CRF) is a common side effect of cancer treatment. A problem identified in most reviews of CRF is lack of sound approaches to measurement that are congruent with the conceptualization of CRF as a self-perceived state. The diversity of instruments available to measure fatigue and the lack of comprehensive testing of several promising instruments with cancer patients undergoing treatment provided the rationale for this study. The purpose of this article is to report the results of psychometric testing of several fatigue instruments in patients undergoing cancer treatment. OBJECTIVES: The aims of this study were to determine the reliability, validity, and responsiveness of each instrument and to determine the ability of each instrument to capture CRF. METHODS: Existing fatigue instruments with published psychometric information that indicated suitability for further testing were selected and included the Profile of Mood States Short Form fatigue subscale (F_POMS-sf), Multidimensional Assessment of Fatigue (MAF), Lee Fatigue Scale (LFS), and the Multidimensional Fatigue Inventory (MFI). Data were collected at a university-based clinical cancer center and a freestanding comprehensive cancer center. Subjects completed all study instruments, which were presented in random order, at a time when CRF was expected to be high and again when it was expected to be low. A subset of subjects completed the instruments within 48 hours of one of the data collection points when CRF was expected to be relatively unchanged to provide stability data. RESULTS: Reliability estimates using Cronbach's alpha indicated that all instruments examined had good internal consistency. Test-retest correlations showed good stability for total scores on all the instruments, but some subscales of the LFS and MFI had marginal stability. Factor analysis of all instruments indicated that only the LFS and the F_POMS-sf fully supported their construct validity. All of the instruments showed responsiveness to changes in CRF related to treatment. CONCLUSIONS: The results of the study provide researchers and clinicians with detailed comparisons of the performance of established fatigue measures in cancer patients undergoing treatment to use when selecting measures of CRF.