Figure 2.

The Golden Gate Bridge is presented as a visual metaphor for the complementary contributions made by different conceptual constructs to the integrity and function of a complex system. A. Phenotypic frailty involves the existence of a specific state or phenotype that is defined by measurable changes involving structures such as a major tower (red) or horizontal cable (red long dash) that perform unique functions and are critical to the existence of the overall system. B. Stochastic frailty is defined as a process whereby the accumulation of deficits involving more redundant structures such as vertical cables (absent or red stippled) raises system vulnerability. C. Resilience evaluates the ability of the system to withstand expected stressors such as bridge traffic, wind and water currents (red arrows). All of these complementary perspectives must be considered when designing a bridge or providing care for older adults. Each approach has its strengths as regards specific questions and further research is needed. However, phenotypic frailty is most helpful when focusing on a specific clinical state associated with increased vulnerability and for measuring the effects of an intervention targeting risk factors or mechanisms that are relatively specific to that condition. Stochastic frailty may be most helpful for individual prognostication and for evaluating interventions that are more pleiotropic or that target shared risk factors or biological mechanisms.