The general notion of frailty is widely understood to be a state of increased vulnerability to stressors, following age-related declines in function and reserves across multiple physiological systems. Frailty is clinically characterised by slower and/or incomplete recovery from stressors such as infection, injury, surgery or psychosocial distress. There is however no consensus on a single operational definition. Numerous assessment tools and scores are promoted to detect or measure frailty but two have widest research background and acceptance, the Frailty Phenotype and the deficit based Frailty Index. We describe these and other approaches in the context of a description of the psychometric properties, types of scaling, uses and misuses of assessment tools. We advocate the choice of an appropriate measurement tool be based on the population characteristics and the purpose for which it is to be used and illustrate how an understanding of the properties of different tools helps to inform this choice.
Keywords: Accuracy; Diagnosis; Epidemiology; Frailty; Fried; Prevalence; Prognosis; Rockwood.