Proxy reports of physical activity were valid in older people with and without cognitive impairment

Objective: To determine the validity of proxy reports of physical activity in people with symptoms of cognitive impairment.

Study design and setting: 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.

Conclusion: Proxy-reported physical activity appears to be a valid estimate of physical activity in people with symptoms or a diagnosis of cognitive impairment.