Table 2.

The findings of the OPV unit root test.

Variables	At Level		At First Differences
	T-Statistics	BD1	Variables	T-Statistics	BD1
OPVt	−4.512	2007	GDPt	−6.495 **	2014
GDPt	−4.231	2014	NRt	7.122**	1992
NRt	−3.51	2003	REt	−5.004 **	2002
REt	3.003	1998	CO2t	−12.511 **	2007
CO2t	−1.644	2002	GFt	−6.452 **	2007