The Karnofsky performance status scale: An examination of its reliability and validity in a research setting

TLDR

The Karnofsky Performance Status Scale is a widely used tool to quantify functional status in cancer patients, yet data on its reliability and validity are limited, and it serves as both an eligibility criterion and outcome measure in the National Hospice Study. Interviewers received intensive training on KPS guidelines and were re‑tested after four months using narrative patient descriptions to assess consistency. The study found excellent interrater reliability (0.97), strong construct validity with two independent functioning measures, and a modest predictive relationship with longevity (r = 0.30), supporting the KPS as a valuable research tool when used by trained observers.

Abstract

The Karnofsky Performance Status Scale (KPS) is widely used to quantify the functional status of cancer patients. However, limited data exist documenting its reliability and validity. The KPS is used in the National Hospice Study (NHS) as both a study eligibility criterion and an outcome measure. As part of intensive training, interviewers were instructed in and tested on guidelines for determining the KPS levels of patients. After 4 months of field experience, interviewers were again tested based on narrative patient descriptions. The interrater reliability of 47 NHS interviewers was found to be 0.97. The construct validity of the KPS was analyzed, and the KPS was found to be strongly related (P < 0.001) to two other independent measures of patient functioning. Finally, the relationship of the KPS to longevity (r = 0.30) in a population of terminal cancer patients documents its predictive validity. These findings suggest the utility of the KPS as a valuable research tool when employed by trained observers.