Proxy measurements in multiple sclerosis: agreement between patients and their partners on the impact of multiple sclerosis in daily life.
BACKGROUND
The use of self-report measurements in clinical settings has increased. The underlying assumption for self-report measurements is that the patient understands the questions fully and is able to give a reliable assessment of his or her own health status. This might be problematic in patients with limitations that interfere with reliable self-assessment such as cognitive impairment or serious mood disturbances, as may be the case in multiple sclerosis. In these situations proxies may provide valuable information, provided we can be certain that proxies and patients give consistent ratings.


OBJECTIVE
To examine whether patients with multiple sclerosis and their partners agree on the impact of multiple sclerosis on the daily life of the patient by using the Multiple Sclerosis Impact Scale (MSIS-29).


METHODS
59 patients with multiple sclerosis and their partners completed the MSIS-29. Agreement was examined, comprehensively at scale score levels and item functioning, using both traditional and less conventional psychometric methods (Rasch analysis).


RESULTS
Agreement between patients and partners was good for the physical scale, and slightly less but still adequate for the psychological scale. Mean directional differences did not show considerable systematic bias between patients and proxies. Intraclass correlation coefficients (ICCs) satisfied the requirements for agreement, but were higher for the physical scale (0.81) than for the psychological scale (0.72). These findings were supported by Rasch analyses.


CONCLUSIONS
In this sample, albeit small, partners provided accurate estimates of the impact of multiple sclerosis. This supports the value of self-rating scales and indicates that partners might be useful sources of information when assessing the impact of multiple sclerosis on the daily life of patients.
van der Linden
F A H
FA
Department of Neurology, VU University Medical Centre, PO Box 7057, 1007 MB Amsterdam, The Netherlands. fah.vdlinden@vumc.nl
Kragt
J J
JJ
Hobart
J C
JC
Klein
M
M
Thompson
A J
AJ
van der Ploeg
H M
HM
Polman
C H
CH
Uitdehaag
B M J
BM
D000328:Adult; D005260:Female; D006304:Health Status; D006801:Humans; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000150:complications*; D015588:Observer Variation; D019727:Proxy; D015203:Reproducibility of Results; D012647:Self-Assessment; D012720:Severity of Illness Index