Timmermans MJ, van Vught AJ, Maassen IT, Draaijer L, Hoofwijk AG, Spanier M, van Unen W, Wensing M, Laurant MG. Determinants of the sustained employment of physician assistants in hospitals: a qualitative study. BMJ Open. 2016 Nov 18;6(11):e011949. doi: 10.1136/bmjopen-2016-011949.