Most conceptual and operational definitions of frailty place heavy emphasis on the physical problems encountered by older people. The accompanying models are based largely on a medical model. An integral approach is almost never adopted. This study aims to develop both an integral operational definition of frailty and an integral conceptual model of frailty. In order to achieve these aims, a thorough literature search was performed on components of operational definitions and models of frailty. In addition, experts (N=17) were consulted during two expert meetings. There was consensus among the experts on the inclusion of the following components in the operational definition of frailty: strength, balance, nutrition, endurance, mobility, physical activity and cognition. Some respondents indicated that they would wish to add components from the psychological or social domain. Supported by results from the literature search, a new integral operational definition of frailty was developed. This operational definition lies at the heart of an integral conceptual working model of frailty. This model expresses the relationships between three domains of frailty, adverse outcomes such as disability and the determinants. The model should be able to serve as a basis for further scientific research on frailty. The model also provides a framework for the development of a measurement instrument which can be used for the identification of frail elderly persons.

Purpose: To assess the predictive validity of frailty and its domains (physical, psychological, and social), as measured by the Tilburg Frailty Indicator (TFI), for the adverse outcomes disability, health care utilization, and quality of life. Design and Methods: The predictive validity of the TFI was tested in a representative sample of 484 community-dwelling persons aged 75 years and older in 2008 (response rate 42%). A subset of all respondents participated 1 year later (N = 336, 69%) and again 2 years later (N = 266, 55%). We used the TFI, the Groningen Activity Restriction Scale assessing disability, seven indicators of health care utilization, and a brief version of the World Health Organization Quality of Life questionnaire (WHOQOL-BREF). The WHOQOL-BREF was assessed in 2008 and 2010; all others were assessed in 2008, 2009, and 2010. Results: The predictive validity of the TFI assessed in 2008 for disability, health care utilization, and quality of life was corroborated by (a) medium to very large associations of frailty with adverse outcomes 1 or 2 years later; (b) mostly good to excellent area under the curve of total frailty; and (c) an increase in predictive accuracy of most adverse outcomes, even after controlling for that same adverse outcome in 2008, and life-course determinants and multimorbidity. Physical frailty was mostly responsible for the predictive validity of the TFI. Implications: This study showed that the TFI is a valid instrument to predict disability, many indicators of health care utilization, and quality of life of older people, 1 and 2 years later.