An econometric approach on production, costs and profit in Romanian coal mining enterprises

Figures & data

Table 1. Estimations of production and profit via econometric models.

	Model 1		Model 2		Model 3
Constant	206.39 (0.65)	−195.60 (−0.75)	240.37 (0.72)	−8.165 (−0.02)	−0.674 (−0.28)	0.378 (0.07)
DC	28.39** (2.21)	47.61*** (3.64)	–	–	–	–
IC	4.63 (0.65)	8.32** (2.64)	–	–	–	–
FC	–	–	−9.31 (−1.25)	3.504 (0.51)	0.294 (0.71)	0.398 (1.16)
VC	–	–	33.09*** (6.73)	36.53*** (3.82)	−0.235 (−0.91)	−0.340 (−1.25)
PR	–	–	24.01*** (4.77)	29.05*** (2.98)	–	–
Q	–	–	–	–	0.006*** (3.46)	0.007*** (4.47)
Prob.>F	0.000	0.000	0.000	0.000	0.000	0.000
Cross-section effects	Fixed	Fixed	Fixed	Fixed	Fixed	Fixed
Time fixed effects	No	Yes	No	Yes	No	Yes
R^2	0.802	0.896	0.799	0.886	0.354	0.534
Observations	72	72	72	72	72	72

Note: The dependent variables are Q in models (1) and (2) and PR in model (3) for firm ‘i’ in the ‘t’ year. Robust t-statistics are in parentheses; *, **, *** indicate statistical significance at 10%, 5% and 1% levels. Prob.>F is the probability of not being fixed effects. For all estimated, models the hypothesis of multicollinearity is investigated using the variance inflation test (VIF). In all cases the VIF values are lower than 3, which indicates low risk of multicollinearity.

Table 2. The estimations of variable costs and profit via econometric models.

	Model 4		Model 5
Constant	−13.54*** (−2.89)	−7.07*** (−4.05)	−7.13 (−1.54)	−10.59 (−1.56)
Q	0.028*** (5.41)	0.021*** (5.34)	0.016** (2.37)	0.023** (2.62)
Q^2	−0.0004*** (−3.91)	−0.00036*** (−3.42)	−0.00002 (−1.49)	−0.00003* (−1.85)
FC	1.01*** (12.08)	0.991*** (6.53)	0.341** (2.07)	0.540* (1.89)
VC	–	–	−0.309** (−2.46)	−0.433** (−2.63)
Prob.>F	0.000	0.000	0.003	0.003
Cross-section effects	Fixed	Fixed	Fixed	Fixed
Time fixed effects	No	Yes	No	Yes
R^2	0.890	0.924	0.369	0.483
Observations	72	72	72	72

Note: Dependent variable is VC in model 4 and PR in model 5 for firm $\mathrm{\text{'}}i\mathrm{\text{'}}$ in the ‘t’ year. Robust t-statistics are in parentheses; *, **, *** indicate statistical significance at 10%, 5% and 1% levels. Prob.>F is the probability of not being fixed effects.

Figure 1. The relationship between variable costs (VC) and production of coal (lignite) (Q).

Figure 2. The relationship between profit (PR) and production of coal (lignite) (Q).