Using structural equation modeling to detect response shift in performance and health-related quality of life scores of multiple sclerosis patients.
OBJECTIVE
To illustrate how structural equation modeling (SEM) can be used for response shift detection with random measurement occasions and health state operationalized as fixed group membership (Study 1) or with fixed measurement occasions and health state operationalized as time-varying covariates (Study 2).


METHODS
In Study 1, we explored seven items of the Performance Scales measuring physical and mental aspects of perceived disability of 771 stable, 629 progressive, and 1,552 relapsing MS patients. Time lags between the three measurements varied and were accounted for by introducing time since diagnosis as an exogenous variable. In Study 2, we considered the SF-12 scales measuring physical and mental components of HRQoL of 1,767 patients. Health state was accounted for by exogenous variables relapse (yes/no) and symptoms (worse/same/better).


RESULTS
In Study 1, progressive and relapsing patients reported greater disability than stable patients but little longitudinal change. Some response shift was found with stable and relapsing patients. In Study 2, relapse and symptoms were associated with HRQoL, but no change and only little response shift was found.


CONCLUSIONS
While small response shifts were found, they had little impact on the evaluation of true change in performance and HRQoL.
Department of Medical Psychology, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands.
Bellinda L
BL
King-Kallimanis
Frans J
FJ
Oort
Sandra
S
Nolte
Carolyn E
CE
Schwartz
Mirjam A G
MA
Sprangers
D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D020528:Multiple Sclerosis, Chronic Progressive / Q000503:physiopathology / Q000523:psychology*; D020529:Multiple Sclerosis, Relapsing-Remitting / Q000503:physiopathology / Q000523:psychology*; D009656:North America; D011788:Quality of Life / Q000523:psychology*; D012042:Registries; D018434:Sickness Impact Profile
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