“…Nonpatient facing physicians such as anesthesiologists, emergency medicine, radiologists, and pathologists were excluded in 11 studies [14,[28][29][30][31][32][33][34][35][36][37]. Studies also varied in geographic scope, ranging from constructing networks by country [20,38,39], hospital referral region [26,28,30,34,40], state [16,21,31,41], city [42,43], or within a hospital or health system [24,25,29,[44][45][46][47][48][49]. The geographic boundaries of a network are important to consider because networks are subject to the boundary specification problem in which excluding certain patients and/or providers may alter the network structure [50].…”