Table 8.

Panel regression test results of DIRS and DIRS² on SR and Tobin's Q.

	Coefficient	t-statistics	p-value
Panel A: SR (pooled OLS)
Constant	6.7029	0.8278	0.4084
DIRS	−0.2993	−0.5381	0.5909
DIRS2	0.0018	0.2070	0.8362
F-statistic = 1.4074 Prob. (F-statistic) = 0.2462			Adjusted R2 = 0.0024 DW = 2.1565
Panel B: SR (pooled OLS)
Constant	55.8207	1.5172	0.1302
DIRS	−0.9726	−1.3481	0.1786
DIRS2	0.0113	1.0454	0.2966
SIZE	−2.6139	−1.3500	0.1780
ΔSALES	0.0957	1.1422	0.2542
F-statistic = 1.4967 Prob. (F-statistic) = 0.2029			Adjusted R2 = 0.0060 DW = 2.1679
Panel C: Tobin's Q (random effects)
Constant	0.3291	6.5998	0.0000**
DIRS	0.0035	1.9936	0.0452*
DIRS2	−0.0000	−3.3666	0.0008**
F-statistic = 16.7400 Prob. (F-statistic) = 0.0000**			Adjusted R2 = 0.0916 DW = 1.5823
Panel D: Tobin's Q (random effects)
Constant	−0.5901	−3.9227	0.0001**
DIRS	0.0078	2.6825	0.0077**
DIRS2	−0.0001	−3.3665	0.0009**
SIZE	0.0522	6.5745	0.0000**
ΔSALES	0.0000	−0.0233	0.9814
F-statistic = 20.6499 Prob. (F-statistic) = 0.0000**			Adjusted R2 = 0.1924 DW = 1.6001

Note: DW is the Durbin–Watson (1950) statistic, $DW={\sum }_{t=2}^N{({\hat{e}}_t-{\hat{e}}_{t-1})}^2/{\sum }_{t=1}^N{\hat{e}}_t^2$ and ${\hat{e}}_t$ are the least squares residuals from the regression equation under consideration. Based on the Durbin–Watson bounds test, there is no residual autocorrelation if DW is greater than the upper critical value bound, which approximately equals 1.78 at the 5% significance level.

^*Represent the significance level of 5%.

^**Represent the significance level of 1%.