The size of the treatment effect: do patients and proxies agree?
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BACKGROUND: This study examined whether MS patients and proxy respondents agreed on change in disease impact, which was induced by treatment. This may be of interest in situations when patients suffer from limitations that interfere with reliable self-assessment, such as cognitive impairment. METHODS: MS patients and proxies completed the Multiple Sclerosis Impact Scale (MSIS-29) before and after intravenous steroid treatment. Analyses focused on patient-proxy agreement between MSIS-29 change scores. Transition ratings were used to measure the patient's judgement of change and whether this change was reflected in the MSIS-29 change of patients and proxies. Receiver operating characteristic (ROC) analyses were also performed to examine the diagnostic properties of the MSIS-29 when completed by patients and proxies. RESULTS: 42 patients and proxy respondents completed the MSIS-29 at baseline and follow-up. Patient-proxy differences between change scores on the physical and psychological MSIS-29 subscale were quite small, although large variability was found. The direction of mean change was in concordance with the transition ratings of the patients. Results of the ROC analyses of the MSIS-29 were similar when completed by patients (physical scale: AUC = 0.79, 95% CI: 0.65-0.93 and 0.66, 95% CI: 0.48-0.84 for the psychological scale) and proxies (physical scale: 0.80, 95% CI: 0.72-0.96 and 0.71, 95% CI: 0.56-0.87 for the psychological scale) CONCLUSION: Although the results need to be further explored in larger samples, these results do point towards possible use of proxy respondents to assess patient perceived treatment change at the group level.
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