Some mathematical models of frailty and their clinical implications

Frailty is a term that is used often, but commonly not defined precisely. As reviewed elsewhere most definitions share several features. Typically, older adults who are frail have a greater rate of dependence on others, so-called ‘loss of physiological reserve’ and multiple diseases. A dynamic component is often included (e.g. ‘loss of reserve’ and such synonyms as ‘unstable disability’ and ‘impaired homeostenosis’) and is manifest when, over time, patients respond less well to stress, or when those with given levels of frailty have higher rates of adverse outcomes. Still, the imprecision of the term frailty has led some to question its merit, and either to develop alternative means of classification or to stay with the concept of function and disability. Alternative methods of classification are either broadly or narrowly focussed.