Abstract
Frailty as a state of increased risk can be operationalized by a frailty index. It is the proportion of age-related health deficits present in an individual to the deficits counted. As it does not require special instrumentation, existing/routinely collected data can quantify frailty across clinical and population settings. Several electronic frailty indices have been devised, allowing risk to be graded on millions of people. The mean frailty index score varies by regional and national economic indicators, so it is also being used as a population health metric. Despite varying versions, the frailty index characteristically increases by ~4% annually across the adult lifespan, to a maximum value of 0.7. It is used in research to estimate personal biological age and more recently in pre-clinical models. From cellular to social inquiries the metrics of the frailty index can grade clinical risk and can facilitate the study of ageing, resilience and age-related illnesses.