Response shift in quality of life measurement in early-stage breast cancer patients undergoing radiotherapy S.J.T. Jansen 1,2 , A.M. Stiggelbout 2 , M.A. Nooij 1 , E.M. Noordijk 1 & J. Kievit 2 1 Department of Clinical Oncology, Leiden University Medical Center, Leiden, The Netherlands; 2 Department of Medical Decision Making, Leiden University Medical Center, Leiden, The Netherlands Accepted in revised form 2 October 2000 Abstract In medicine, response shift refers to a change ± as a result of an event such as a therapy ± in the meaning of one's self-evaluation of quality of life. Due to response shift, estimates of side eects of radiotherapy may be attenuated if patients adapt to treatment toxicities. The purpose of our study was to assess to what extent two components of response shift, scale recalibration and changes in values, occur in early-stage breast cancer patients undergoing radiotherapy and to examine what the implications would be for treatment evaluation. In the week before start of post-operative radiotherapy, 46 patients ®lled out a questionnaire consisting of quality of life items of the SF-36 and the Rotterdam symptom checklist (RSCL) (pretest). During radiotherapy, patients were asked to ®ll out the questionnaire twice: a posttest (quality of life at that moment) and a thentest (quality of life before treatment, retrospectively), supposedly using the same internal standard. Changes in values were studied by asking the patients on the two occasions to rate the importance of seven attributes representing various domains of quality of life. Patients were also asked whether their quality of life with respect to the measured aspects had changed since the pretest (subjective transition scores). Signi®cant scale recalibration eects were observed in the areas of fatigue and overall quality of life. When the groups were divided according to their subjective transition scores, signi®cant scale recalibration eects were found in case of worsened quality of life for fatigue and overall quality of life, and in case of improved quality of life for fatigue and psychological well-being. The mean importance ratings remained fairly stable over time, except for `skin reactions', which obtained less importance at the end of radiotherapy than before. In conclusion, eects of scale recalibration were observed that would have signi®cantly aected quality of life evaluations, in that the impact of radiotherapy on fatigue and overall quality of life would have been underestimated. Changes in internal values were observed only for `skin reactions'. Key words: Quality of life, Radiotherapy, Response shift Introduction ``Now I know what `exhausted' means. Before treatment I thought I was exhausted, but now I realize I was merely tired at that time''. In medi- cine, self-report questionnaires are used frequently for measuring the quality of life of patients over time, for example in breast cancer patients undergoing post-operative radiotherapy. However, recent developments in quality of life research have shown that changes in health status may induce changes in the meaning of one's self-eval- uation: a phenomenon called response shift [1]. Schwartz and Sprangers [1] use as a working def- inition of response shift: `¼ response shift refers to a change in the meaning of one's self-evaluation of a target construct as a result of: (a) a change in the respondent's internal standards of measure- ment (i.e. scale recalibration); (b) a change in the respondent's values (i.e. the importance of Quality of Life Research 9: 603±615, 2000. Ó 2001 Kluwer Academic Publishers. Printed in the Netherlands. 603