Aims: There are situations in which patient self-reported health-related quality of life must be substituted by proxy assessments. Pickard and Knight recently delineated 2 proxy perspectives that may influence the nature of proxy measurements: the "proxy-patient" (the proxy's assessment from the patient's perspective) and the "proxy-proxy" perspective (the proxy's own assessment of the patient). They argued that the "proxy-patient" perspective would be " optimally consistent with the patient's view." The purpose of this study was to evaluate these to proxy perspectives in terms of patient-proxy bias and agreement.
Methods: The European Organization for Research and Treatment of Cancer Quality of Life Questionnaire-C30 was administered to 224 cancer patients and their proxies (ie, significant others), who were randomly assigned to 1 of the 2 proxy conditions. Differences in patient-proxy bias and agreement were evaluated using t tests, percentage agreement, and intraclass and Pearson correlation coefficients.
Results: Small yet significant amounts of patient-proxy bias were found in both conditions, with patients reporting higher levels of functioning and lower symptoms levels than proxies. However, no significant differences in bias were observed between the conditions. Significantly better agreement on the role and cognitive functioning scales was found in the "proxy-proxy" condition, and for the diarrhea scale in the "proxy-patient" condition.
Conclusions: There is some indication that several of the European Organization for Research and Treatment of Cancer functional scales may perform better when using the "proxy-proxy" perspective. However, no compelling evidence was found for clear superiority of either proxy perspective. These results deserve further study, as they are not entirely consistent with the pattern of agreement implied by Pickard and Knight.