Frailty: enhancing the known knowns.

Every man desires to live long, but no man would be old. Understanding frailty—the concept of vulnerability to adverse health outcomes of people of the same chronological age—continues to motivate research by geriatricians, epidemiologists, sociologists and laboratory-based scientists. While some clinicians have embraced frailty as the Holy Grail of geriatric medicine [1] or advocated it as another Geriatric Giant [2], others remain unconvinced about the feasibility of applying frailty measures in routine practice [3]. The potential to measure with precision the vulnerability of older people has been met with skepticism [4]. Some geriatricians suspect that objective frailty measures are meant to undermine clinical judgement, somehow reflecting an erosion of trust between patients and their doctors [5]. Moreover, efforts to underpin geriatric medicine with more scientific rigour have not been accompanied by reduced antipathy to our specialty [6]. The frailty index (FI), or deficit accumulation model, is one of the three main approaches to the measurement of frailty. It conceptualises frailty as a multidimensional risk state, which can be measured by the quantity rather than by the nature of health problems; individuals accumulate deficits throughout their lives and the more things individuals have wrong with them, the higher the likelihood they will be frail [7]. The FI employs a well-defined methodology (e.g. someone with 6 deficits out of 40 counted has a FI of 0.15). Alternative approaches are to identify frailty as a clinical syndrome or phenotype (such as that defined by Fried et al. [8] as the presence of ≥3 of 5 criteria: weight loss, exhaustion, weak grip strength, slow walking speed and low physical activity) or the measurement of frailty based on the clinician's subjective opinion [9]. The former predicts adverse outcomes in large population samples [10]. The latter have strong face validity, but rely on judgement and depend on geriatric expertise (e.g. accurate assessment of functional status) limiting their generalisability. Most FI studies have been conducted in North America; similar FI properties have been described in samples from Canada [11], the USA [12] and China [13]. Examining frailty across other populations would contribute to the 'known knowns' of frailty. The accompanying paper [14] is the most comprehensive investigation to date of the FI in Europe. The Survey of Health, Ageing and Retirement in Europe (SHARE) is a large cohort study of 29,905 community-dwelling participants aged over 50 years (mean 64 years) from 12 European countries was determined for …