Table 3. Estimated coefficients of the fitted quadratic polynomial equations for dependent variables based on t-statistic

Parameters		Constant	X1	X2	X1X1	X2X2	X1X2
Y	Coefficient	7.2330	0.2561	0.4018	−0.4042	−0.0042	−0.3000
	p-value	0.000	0.013	0.002	0.004	0.961	0.026

X₁, barrel temperature (°C); X₂, screw speed (rpm); Y, overall acceptance (points).