206
Tạp chí
Kinh tế - Kỹ thuật
3.2.3. Control variables
Industry
Industrial related factors represent a relevant variable to explain the divergences in firms’
environmental performance. Because different industrial sectors have different pollution potentials,
firms in different sectors will be subject to different pressures from environmental stakeholders.
These industrial characteristics can explain the heterogeneity of firms’ green product diversification
practices (Banerjeeet al., 2003; Wagner, 2007; González-Benito and González-Benito, 2010).
Firm size
The different researchers consider that the larger the firms, the more resources and abilities to
reduce environmental impacts (Melnyket al., 2003). Hence, firms’ size is considered in our study
in analyzing firms’ decision to adopt green product diversification.
Based on previous studies (Aragón-Correa, 1998; Melnyket al., 2003; Wagner, 2007; González-
Benito and González-Benito, 2010), we use the number of employees as a measurement of firms’
size. We distinguish between micro firms (1-9 employees; reference category), small firms
(10-49 employees) and medium-sized firms (50-300 employees).
This distinction corresponds
to the definition of SMEs set by the Vietnamese government and the World Bank. Several studies
show that firms’ size has a positive effect on firms’environmental activities in general (Melnyket
al., 2003; Zhu et al., 2008) and on green product in particular (Rehfeldet al., 2007).
4. RESULTS AND ANALYSIS
Certification status of ISO 14001 during 2010–2014 is used as the proxy variable to measure
vertical green product diversification, and the certification status of eco-label during 2010–2014 as
the proxy variable to measure horizontal green product diversification, both as the dependent and
dummy variables in the study. Based on the dependent variables, binary discrete choice model is
applied. The independent variables include: ENT (entrepreneur), REG (regulation), FDI (foreign
direct invetement), GDPPC (GDP per capital income), EXPORT, and SIZE. Except the dummy
independent variables, the independent variables are lagged behind by one year to represent the
response time to cater for the variables’ effects (Nishitani, 2009). Based on the previous study
conducted by Christmann and Taylor (2001), the industries with the largest numbers of firms
certified for ISO 14001 and eco-label were nominated as the control.
Table 1: Descriptive statistics and correlations
Variable
Mean
Std.Dev.
1
2
3
4
5
6
7
8
1 Horizontal 0.01
0.11
1
2 Vertical
0.03
0.17
0.11*
1
3 ENT
0.04
0.20
0.00
0.06*
1
4 REG
106.1
6.67
0.01
-0.02
-0.03
1
5 FDI
0.11
0.31
0.01
0.07*
-0.00
0.00
1
6 GDPPC
14023
8029
0.01
0.01
0.016
-0.05
0.10* 1
7 EXPORT
0.42
0.49
0.04*
0.06*
0.06*
-0.03
0.15* -0.04* 1
8 SIZE
727.8
3149
0.11*
0.13*
0.024
0.04
-0.02 -0.07* 0.11* 1
*p<0.1,**P<0.05.
The statistics of explanatory variables and dependent variables used for analysis are summarized
in Table 1.
