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Open Access Research article

The size of the treatment effect: do patients and proxies agree?

Femke AH van der Linden12*, Jolijn J Kragt1, Jeremy C Hobart45, Martin Klein2, Alan J Thompson4, Henk M van der Ploeg2, Chris H Polman1 and Bernard MJ Uitdehaag13

Author Affiliations

1 Department of Neurology, VU University Medical Centre, Amsterdam, The Netherlands

2 Medical Psychology, VU University Medical Centre, Amsterdam, The Netherlands

3 Clinical Epidemiology and Biostatistics, VU University Medical Centre, Amsterdam, The Netherlands

4 Neurological Outcome Measures Unit, Institute of Neurology, London, UK

5 Peninsula Medical School, Derriford Hospital, Plymouth, UK

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BMC Neurology 2009, 9:12  doi:10.1186/1471-2377-9-12

Published: 25 March 2009

Abstract

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.