Summary of the methodological constructs of the four frailty indexes compared.

FI-SOF: Frailty Index derived from the Study of Osteoporotic Fractures;FI-CD: Frailty Index based on cumulative deficits;FI-CGA: Frailty Index based on a Comprehensive Geriatric Assessment;ADL: activities of daily living;IADL: instrumental activities of daily living;SPMSQ: Short Portable Mental Status Questionnaire;CIRS: Cumulative Illness Rating Scale;MNA: Mini Nutritional Assessment;ESS: Exton-Smith Scale;MPI: Multidimensional Prognostic Index.