Differences in proxy-reported and patient-reported outcomes: assessing health and functional status among medicare beneficiaries.
BACKGROUND
Proxy responses are very common when surveys are conducted among the elderly or disabled population. Outcomes reported by proxy may be systematically different from those obtained from patients directly. The objective of the study is to examine the presence, direction, and magnitude of possible differences between proxy-reported and patient-reported outcomes in health and functional status measures among Medicare beneficiaries.


METHODS
This study is a pooled cross-sectional study of a nationally representative sample of community-dwelling Medicare beneficiaries from 2006 to 2011. Survey respondents can respond to the Medicare Current Beneficiary Survey either by themselves or via proxies. Health and functional status was assessed across five domains: physical, affective, cognitive, social, and sensory status. Propensity score matching was used to get matched pairs of patient-reports and proxy-reports.


RESULTS
After applying the propensity score matching, the study identified 7,780 person-years of patient-reports paired with 7,780 person-years of proxy-reports. Except for the sensory limitation, differences between proxy-reported and patient-reported outcomes were present in physical, affective, cognitive, and social limitations. Compared to patient-reports, a question regarding survey respondents' difficulties in managing money was associated with the largest proxy response bias (relative risk, RR = 3.83). With few exceptions, the presence, direction, and magnitude of differences between proxy-reported and patient-reported outcomes did not vary much in the subgroup analysis.


CONCLUSIONS
When there is a difference between proxy-reported and patient-reported outcomes, proxies tended to report more health and functional limitations among the elderly and disabled population. The extent of proxy response bias depended on the domain being tested and the nature of the question being asked. Researchers should accept proxy reports for sensory status and objective, observable, or easy questions. For physical, affective, cognitive, or social status and private, unobservable, or complex questions, proxy-reported outcomes should be used with caution when patient-reported outcomes are not available.
Department of Clinical Pharmacy and Outcomes Sciences, South Carolina College of Pharmacy, University of South Carolina, 715 Sumter Street, Columbia, SC, USA. minghui@email.sc.edu.
Minghui
M
Li
Department of Pharmaceutical Health Services Research, School of Pharmacy, University of Maryland, 220 Arch Street, Baltimore, MD, USA. iharris@impaqint.com.|IMPAQ International, LLC, 10420 Little Patuxent Pkwy, Columbia, MD, USA. iharris@impaqint.com.
Ilene
I
Harris
Department of Clinical Pharmacy and Outcomes Sciences, South Carolina College of Pharmacy, University of South Carolina, 715 Sumter Street, Columbia, SC, USA. luk@sccp.sc.edu.
Z Kevin
ZK
Lu
D000368:Aged; D000369:Aged, 80 and over; D015982:Bias; D003430:Cross-Sectional Studies; D005260:Female; D006304:Health Status; D006306:Health Surveys / Q000379:methods* / Q000592:standards; D006801:Humans; D008297:Male; D006278:Medicare / Q000706:statistics & numerical data; D008875:Middle Aged; D017063:Outcome Assessment, Health Care / Q000379:methods* / Q000592:standards; D019727:Proxy; D015203:Reproducibility of Results; D057566:Self Report; D014481:United States