We thank Dr. Yilmaz and colleagues [1] for their comment that allows us to further clarify a major strength of the BIOSPHERE study [2]. Many operational definitions of frailty exist, each of them describing specific aspects of the condition and capturing different risk profiles. The two constructs mentioned by the authors (i.e., the phenotype proposed by Fried et al. [3] and the FRAIL criteria designed by Morley [4]) are not gold standards for the assessment of physical frailty, simply because no reference tool is recognized in this field.
