Theoretical model of the association of life space with the clinical syndrome of frailty. Solid and dashed lines represent direct and indirect effects, respectively; arrows represent causal direction. (Xue QL, Fried LP, Glass TA, et al. Life-space constriction, development of frailty, and the competing risk of mortality: the Women’s Health And Aging Study I. Am J Epidemiol 2008;167(2):240–8, by permission of Oxford University Press.)