	(1)	(2)	(3)	(4)
VARIABLES	South-North;North-South;South-South;North-North	South-North;North-South;South-South;North-North	South-North;North-South;South-South;North-North	South-North;North-South;South-South;North-North
				
dsps	-0.007**	-0.006	0.002	-0.014***
	(0.003)	(0.004)	(0.012)	(0.005)
ltariff	-0.000	-0.002*	-0.001	0.000
	(0.001)	(0.001)	(0.002)	(0.001)
rta	0.006**	-0.003	0.023*	0.008
	(0.003)	(0.007)	(0.013)	(0.008)
Constant	0.046***	0.081***	0.074***	0.092***
	(0.002)	(0.003)	(0.005)	(0.003)
				
Observations	18,352	19,968	15,770	22,123
R-squared	0.884	0.957	0.882	0.955
Robust standard errors in parentheses				
*** p<0.01, ** p<0.05, * p<0.1				
