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(Stroke. 2002;33:2593.)
© 2002 American Heart Association, Inc.

Original Contributions

Evaluation of Proxy Responses to the Stroke Impact Scale

Pamela W. Duncan, PhD, FAPTA; Sue Min Lai, PhD, MS, MBA; Denise Tyler, MA; Subashan Perera, PhD; Dean M. Reker, PhD, RN Stephanie Studenski, MD, MPH

From the Brooks Center for Rehabilitation Studies, University of Florida, and Rehabilitation Outcomes Research Center, North Florida/South Georgia Department of Veteran Affairs, Gainesville, Fla (P.W.D.); Kansas City Department of Veterans Affairs Medical Center, Kansas City, Mo (D.T., D.M.R.); and Center on Aging, University of Kansas Medical Center, Kansas City, Ks (P.W.D., S.M.L., S.P., D.M.R., S.S.).

Correspondence to Pamela W. Duncan, PhD, FAPTA, Brooks Center for Rehabilitation Studies, College of Health Professions, University of Florida, Health Science Center, Box 100185, Gainsville, FL 32610-0185. E-mail pwduncan{at}hp.ufl.edu

Background and Purpose— The purposes of this study were to compare proxy-patient responses on each domain of the Stroke Impact Scale (SIS) and the SIS-16, estimate the bias, and evaluate the validity of proxy scores.

Methods— Two hundred eighty-seven patient and proxy pairs from the Kansas City Stroke Registry participated in the study. All patients were assessed in their home or nursing facility between 90 and 120 days after stroke with the use of the modified Rankin Scale Motricity Index (strength), Barthel Index (activities of daily living), Lawton assessment (instrumental activities of daily living), Folstein Mini-Mental State Examination (cognition), and the SIS. Eligible proxies were individuals who were aged 18 years, had known the patient for at least 1 year, and saw the patient at least once each week. All proxy interviews were conducted within 7 days of (before or after) the patient’s interview.

Results— Three hundred seventy-seven patients from the Kansas City Stroke Registry were eligible for the study. Seventy-seven patients or proxies refused participation. Thirteen patients of the consenting patient-proxy pairs were too aphasic or cognitively impaired to complete the interviews and were dropped from the study. Proxies scored patients as more severely affected than patients scored themselves on the SIS-16 and in 7 of 8 domains of the full SIS (5 were statistically significant at =0.05). The proxy bias toward overrating the severity of the patient’s condition tended to increase as the severity of the stroke increased. However, the magnitude of the biases between patient and proxy means, as measured by effect size, was small (range, -0.1 to 0.4). The strength of the agreement, as measured by intraclass correlation coefficients, between proxy and patient ranged from 0.50 to 0.83. Agreement was best for the observable physical domains. Both patient and proxy scores in all domains were significantly different across Rankin categories. Concurrent validity for both patient and proxy correlations with the Folstein Mini-Mental State Examination, Barthel Index, Lawton instrumental activities of daily living, and Motricity Index was good to excellent (range, 0.37 to 0.78).

Conclusions— Proxies provide valid information for assessment of stroke outcomes. There are significant differences between patient and proxy reporting on SIS domains and the SIS-16. However, the observed biases are small and not clinically meaningful.

Key Words: disability evaluation • outcome • quality of life • stroke

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