The Linkage between Imported Energy and Trade in Taiwan

Table 3

Results of unit root tests.

Variable	IM	EX	ENERGY	COAL	OIL	GAS	EX_I	EX_HI	EX_NHI
Level
ADF
𝑇𝑢	−2.23	−1.65	−1.58	−2.28	−2.62	−5.43^***	−1.63	−1.23	−2.34
𝑇𝑡	−2.79	−3.84^**	−3.76^**	−4.58^***	−4.14^***	−5.55^***	−3.80^**	−3.56^**	−2.97
𝑇	0.12	0.63	1.32	0.46	1.00	0.03	0.65	0.90	−0.55
PP
𝑇𝑢	−4.92^***	−1.99	−2.94^**	−3.89^***	−2.94^**	−6.02^***	−1.94	−1.39	−8.22^***
𝑇𝑡	−6.18^***	−5.85^***	−5.23^***	−7.51^***	−5.71^***	−6.10^***	−5.79^***	−5.29^***	−8.64^***
𝑇	0.28	1.23	0.64	0.58	1.36	−0.06	1.30	1.62	−0.24
First difference
ADF
𝑇𝑢	−14.54^***	−18.64^***	−3.20^**	−13.07^***	−3.84^***	−17.86^***	−18.67^***	−18.21^***	−3.32^**
𝑇𝑡	−14.49^***	−18.58^***	−3.21	−13.03^***	−3.86^**	−17.89^***	−18.60^***	−18.15^***	−3.41
𝑇	−14.58^***	−18.59^***	−2.82^***	−13.07^***	−17.47^***	−17.92^***	−18.61^***	−18.10^***	−3.31^***
PP
𝑇𝑢	−29.08^***	−26.19^***	−17.03^***	−28.54^***	−23.22^***	−18.02^***	−25.57^***	−22.45^***	−60.55^***
𝑇𝑡	−29.57^***	−26.33^***	−16.90^***	−28.70^***	−23.51^***	−18.09^***	−25.69^***	−22.38^***	−84.14^***
𝑇	−28.76^***	−22.43^***	−17.01^*	−27.23^***	−22.20^***	−18.08^***	−22.19^***	−19.39^***	−61.41^***

Note: (1) ^*** and ^** represent significance at the 1% and 5% levels, respectively.
(2) The numbers shown in this table represent 𝑡-value. 𝑇_𝑢, 𝑇_𝑡, and 𝑇, respectively, denote the test equation computed with intercept, with linear trend and intercept and without intercept and linear trend. ADF and PP stand for augmented Dickey-Fuller and Phillips and Perron unit root tests, where the same critical values at 5% are −2.86, −3.14, −1.94 and at 1% are −3.43, −3.96, −2.57, respectively.