“…28,38 Thirteen studies studied quality of care 16,20,21,26,28,29,[33][34][35]37,41,48,54 of which five (38 percent) used a difference-in-differences specification. 16,28,29,34,35 Health care spending was evaluated by eight studies 12,16,20,31,35,43,44,48 of which five (63 percent) used a difference-in-differences specification. 12,16,35,43,44 Thirteen studies evaluated the association of tort reform with physician supply 24,27,30,32,34,36,39,40,42,45,46,50,53 of which nine (69 percent) used a difference-in-differences specification.…”