Personalized physiotherapy in frail older adults with mobility problems is (cost)-effective in improving physical activity and frailty: a RCT. (May 2015) - de Vries, N.M.; Staal, J.B.; van der Wees, P.J.; Akkermans, R.; Adang, E.; Rikkert, M.G.M. Olde; Sanden, M.W.G. Nijhuis-Van der