How response shift may affect the measurement of change in fatigue

If patients experience extreme fatigue during treatment, they may judge the level of fatigue following this experience differently from how they would have judged it before. This change in internal standard is referred to as a responsible shift. We explored whether a response shift might have occurr ed in patients receiving radiotherapy (n = 199). Fatigue was assessed befor e and after radiotherapy. Following completion of the post-test, a thentest was administered where patients had to provide a renewed judgement of thei r pre-treatment level of fatigue. Response shift was assessed by the mean d ifference between the pre-test and thentest scores. Comparing the thentest with the pretest scores, patients retrospectively minimized their pre-treat ment level of fatigue. The thentest-post-test difference was significant, w hereas the conventional pretest-post-test difference was not. These results are in line with the occurrence of a response shift. Additional hypotheses regarding response shift were partially supported. It is concluded that th e potentially large implications of response shift justify further research . (C) U.S. Cancer Pain Relief Committee, 2000.