Using proxies to evaluate quality of life. Can they provide valid information about patients' health status and satisfaction with medical care?

Instruments using interview data to measure health status have been increasingly used to measure patient outcomes. To assess the potential utility of proxy responses about health status when subjects are unable to respond, the authors compared the responses of 60 subject and proxy pairs on instruments measuring overall current health, functional status, social activity, emotional health, and satisfaction with medical care. Proxies were asked to respond as they thought the subject would. Subject and proxy responses were strongly correlated with each other for overall health, functional status, social activity, and emotional health (P less than .001), and moderately correlated for satisfaction (P less than .005). Proxies reported lower emotional health and satisfaction than did subjects (P less than .005). Proxy and subject mean responses were generally similar for overall health, functional status, and social activity. However, those proxies who spent more time per week helping the subject rated the subject's functional status and social activity as more impaired than did the subject (P less than .05). Subjects who had poorer overall health tended to rate their health relatively lower than did the proxies (P less than .05). These results suggest that use of proxies intermingled with subjects to measure health status through interview may lead to biased results.