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What Do Osteoarthritis Health Outcome Instruments Measure? Impairment, Activity Limitation, or Participation Restriction?
BETH POLLARD, MARIE JOHNSTON, and PAUL DIEPPE ABSTRACT. Methods. Ten expert judges allocated 342 items from 13 instruments to one or more ICF construct, i.e., Impairment (I), Activity Limitation (A), and Participation Restriction (P). One-sample t tests were used to classify each item as measuring uniquely I, A, or P or some combination (i.e., IA, IP, AP, or IAP). Results. Overall, 12 of the 13 instruments had items that measured a combination of outcome domains (i.e., IA, IP, AP, or IAP). Only the American Knee Society Score (AKS) had all items uniquely measuring either I or A. The instrument with the best representation of items for Impairment was the AKS, for Activity Limitation the WOMAC and Lequesne knee index, and for Participation Restriction the Disease Repercussion Profile. Conclusion. All the existing OA outcome instruments, except one, had some items that were assessing more than one health outcome. Use of these instruments may either mask true treatment effects or make an effect difficult to attribute if the content is unclear. We determined which instruments were the best for measuring each health outcome. To improve the assessment of health outcomes in OA, new instruments that uniquely measure the 3 ICF constructs should be developed and all 3 should be included in relevant studies. (First Release Dec 15, 2005; J Rheumatol 2006;33:757–63)
Key Indexing Terms: OUTCOME MEASURES
From the School of Psychology, University of Aberdeen, Aberdeen; and MRC Health Services Research Collaboration, Department of Social Medicine, University of Bristol, Bristol, United Kingdom. Funded by MRC HSRC Programme Grant "Towards Trials of Joint Replacement." B. Pollard, MSc, Senior Research Fellow; M. Johnston, PhD, Professor of Psychology; P.A. Dieppe, MD, FRCP, Director, MRC Health Services Research Collaboration. Address reprint requests to B. Pollard, School of Psychology, University of Aberdeen, Aberdeen AB24 2UB, UK. Accepted for publication August 29, 2005.
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