title: Proxy reports of physical activity were valid in older people with and without cognitive impairment.
abstract: OBJECTIVE
  To determine the validity of proxy reports of physical activity in people with symptoms of cognitive impairment.
  
  
  METHODS
  In the Canadian Study of Health and Aging, a multicenter prospective cohort study, someone close to the participant (proxy) reported exercise levels for people who screened positive for cognitive impairment or were institutionalized (n=2421), some of whom were subsequently diagnosed with cognitive impairment (n=1612) and some of whom were diagnosed as having no cognitive impairment (n=809). The reliability and validity of proxy reports of physical activity were examined by agreement with self-reports of physical activity (intraclass correlation coefficient) and by association with adverse health markers (Mantel-Haenzel chi(2)) and survival time (Cox proportional hazards).
  
  
  RESULTS
  Proxy reports of physical activity had moderate interrater reliability (0.55, 95% confidence interval: 0.49-0.61, P<0.001). People in higher physical activity group had fewer adverse health outcomes than those in lower physical activity groups. Predictive validity was confirmed as people who had higher proxy-reported physical activity survived longer that those with lower physical activity.
  
  
  CONCLUSIONS
  Proxy-reported physical activity appears to be a valid estimate of physical activity in people with symptoms or a diagnosis of cognitive impairment.
authors.affiliation: Department of Psychiatry, University of California - San Francisco, San Francisco, CA, USA.
authors.forename: Laura E
authors.initials: LE
authors.lastname: Middleton
authors.forename: Susan A
authors.initials: SA
authors.lastname: Kirkland
authors.forename: Arnold
authors.initials: A
authors.lastname: Mitnitski
authors.forename: Kenneth
authors.initials: K
authors.lastname: Rockwood
mesh_terms: D000368:Aged; D002170:Canada / Q000453:epidemiology; D003072:Cognition Disorders / Q000453:epidemiology*; D016001:Confidence Intervals; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D008297:Male; D005082:Physical Exertion; D016016:Proportional Hazards Models; D019727:Proxy; D015203:Reproducibility of Results