Assessing responsiveness of cancer-related fatigue instruments: Distribution-based and individual anchor-based methods

Background. The aims of the study were to examine the responsiveness of Chinese versions of the Cancer Fatigue Scale (C-CFS), the Schwartz Cancer Fatigue Scale-revised (C-SCFS-r), and the Fatigue Symptom Inventory (C-FSI) based on effect sizes and patient perceptions of change. Method. Convenience sampling was used to recruit subjects at a chemotherapy treatment center for outpatients in Taiwan. Data were collected twice: on the day cancer patients were receiving chemotherapy treatment (T1) and 2 days post-treatment (T2). Results. Questionnaires were complete at T2 by 148 subjects (60.9%). The differences between T1 and T2 were statistically significant for all three scales. The effect sizes, ranging from a medium to a large change for the C-CFS, C-SCFS-r, and C-FSI were reported based on four groups (self-reported no increase, small increase, moderate increase, and large increase). Generalized estimating equations were used to compare the fatigue scores based on the four groups by controlling for the fatigue level at baseline and the time effect. The results indicate that the fatigue scores after 2 days of treatment in the three "change" groups were statistically significantly larger than in the "no increase" group. In addition, the pretreatment fatigue level in the "large increase" group was significantly higher than in the other three groups. Conclusion. Results indicate that the three scales are sensitive to change over 2 days. However, the three scales may not effectively discriminate between a moderate and large change. Therefore, further testing on cancer patients with severe fatigue to examine responsiveness to detect minimal important differences for the three scales is recommended.