BACKGROUND AND OBJECTIVES: The relationship between frailty and disability in activities of daily living (ADLs) can be seen in different ways, with disability being-to varying degrees-a characteristic, negative outcome, or predictor of frailty. This conflation of definitions is partly a result of the different frailty tools used in research. Aiming to provide a comprehensive overview, this systematic literature search analyzed (i) if, (ii) to what extent, and (iii) how ADLs are evaluated by frailty instruments.
RESEARCH DESIGN AND METHODS: A search was performed in PubMed, Web of Knowledge, and PsycINFO to identify all frailty instruments, followed by categorization of the ADL items into basic (b-), instrumental (i-), and advanced (a-) ADLs.
RESULTS: In total, 192 articles described 217 frailty instruments, from which 52.1% contained ADL items: 45.2% b-ADLs, 35.0% i-ADLs, and 10.1% a-ADLs. The most commonly included ADL items were bathing (b-ADLs); using transportation (i-ADLs); and semiprofessional work engagement in organized social life or leisure activities (a-ADLs). These instruments all had a multidomain origin (χ 2 = 122.4, p < .001).
DISCUSSION AND IMPLICATIONS: Because 52.1% of all instruments included ADL items, the concepts of frailty and disability appear to be highly entangled. This might lead to circular reasoning, serious concerns regarding contamination, and invalid research results.