Table 1: Summary statistics.

  Variables   Mean   Std.   ADF-test   Obs
lnRGI   6.68   0.80   -1.43   52M
lnWTIOIL   4.51   0.19   -0.57   52M
lnDQOIL   6.31   0.20   -0.20   52M
lnBJCOAL   4.56   0.23   -0.31   52M
lnQHDCOAL   6.17   0.19   -0.71   52M
R_RGI   6.12   5.98   -3.03**   51M
R_WTIOIL   -0.99   7.25   -4.88***   51M
R_DQOIL   -1.05   4.35   -4.62***   51M
R_BJCOAL   -1.31   4.08   -5.64***   51M
R_QHDCOAL   -0.98   4.96   -6.50***   51M

Note: ***, ** and * denote significance at 1%, 5% and 10% levels, respectively.