September 31
st
, 2020, for the period of 1985-2019, 
under the classification of SITC Rev.1 from United 
Nation Comtrade database (available from: 
https://comtrade.un.org/data/). There are six 3-digit 
energy products involved which includes "coal, coke 
and briquettes" (code 321), "petroleum, crude and 
partly refined" (code 331), "petroleum products" 
(code 332), "gas, natural and manufactured" (341), 
"electric current" (code 351) and "mineral tar" (code 
521) (Chen, 2020). Some countries’ delayed data 
reporting to UN Statistics Division makes the data 
for 2019 and for the recent years only partially 
available. As a result, later accession may generate 
slightly different data. 
2.2  Indicators for the Trade Patterns 
This study employed the indicators of "trade 
competitiveness" (TC) and then used the indicator of 
export promotion (HX) which is derived from TC 
and the indicators of "revealed symmetric 
comparative advantage for export" (RX), to examine 
the Chinese trade patterns in energy export. 
•  Trade Competitiveness. The indicator is a 
county's trade balance in proportion to the total 
import and export value in product k: 
TC
ck 
= (X
ck
 - M
ck
)/ (X
ck
 + M
ck
)           (1) 
where X stands for export value and M is for the 
value of import. The subscript of c indicate that the 
reporting country is China and the subscript of k 
represents each specific 3-digit energy product. The 
value range of TC
ck
 is [-1, 1] with a mean of zero. 
•  Revealed comparative advantage. Balassa 
(1965) designed the indicator to measure one 
comparative advantage that revealed in the trade of 
product k (Balassa, 1965). 
RCA
ck 
= (X
ck
 / X
wk
)/ (X
c
 / X
w
)        (2) 
where X
c
 is the total trade value of country c and the 
subscript of w is for the world. The indicator of 
RCA
ck
 compares product k's share in country c to 
that in the world total export (X
w
). RCA
ck
 ranges 
from 0 to X
w
/X
c
 without a certain upper bound and a 
certain mean, preventing the comparing across 
different countries, products and other indicators of 
trade patterns. 
•  Revealed symmetric comparative advantage. 
Dalum, Laursen and Villumsen (1998) proposed the 
indicator of "revealed symmetric comparative 
advantage" (RSCA) to address RCA's problems of 
uncertain value range and definite mean (Dalum, 
1998) by 
RX
ck
=RSCA
ck 
= (RCA
ck
 - 1)/ (RCA
ck
 + 1)     (3) 
which has the range of [-1, 1] with a mean of zero, 
being identical to that of TC
ck
 (Hong, 2018; Hong, 
2010; Shi, 2019). This study added X to indicate the 
"revealed symmetric comparative advantage" is for 
the energy export. 
•  Policy intervention in export. In Ricardian 
comparative advantage theory, a country should 
specialize in and export the products in which she has 
comparative advantage, and import the products in 
which the country is dis-comparative advantaged. 
The higher degree of comparative advantage in 
product k implies country c's more export in the 
product and vice versa. Under perfect free trade 
environment where there is no any government 
policy intervention, the equilibrium of 
TC
ck
=RX
ck
 (4) 
must hold. This deduction facilitates the measuring 
of policy intervention in the trade by 
HX
ck
=TC
ck 
- RX
ck
 (5) 
where HX
ck
 is country c's policy intervention in 
product k's export with the value range of [-2, 2]. 
HX
ck
>0 implies that country c promotes the export 
in product k, making the indicator of TC
ck
 higher 
than the export comparative advantage; HX
ck
<0 
means export restriction (Pang, 2010). 
•  Weighting approaches. Because there are six 
3-digit specific energy products, weighting is 
necessary to obtain the indicators of the trade 
patterns for the product category j. We used the 
proportion of country c in the world total export 
value of product k, or  
w
1
=X
ck 
/ X
wk
 (6) 
to weight RX
ck
 because only export is involved here. 
The weight for the HX
ck
 is  
w
2
=(X
ck
 + M
ck
)
 
/ (X
wk
 + M
wk
)              (7) 
because both the export and the import are necessary 
to obtain the indicator of HX
cj
. 
2.3 Econometric Analyses 
Different approaches should be employed according 
to the generating process of the time series of RX
ck
 
and HX
ck
 in order to avoid any conjecture. This 
research performed augmented Dicky-Fuller (ADF) 
unit root tests to examine the stationarity of the time 
series; we employed the least information criteria of 
the vector auto-regression (VAR) models to select 
between the linear or non-linear model assumptions 
as well as the VAR lag interval; this research made 
vector error correction (VEC) models select the