Table 5.

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

Parameters	Y1 Rupture Strength (kPa)
	Coefficient	Square Error	t-Value	p-Value
Constant	3090	110	28.07	0.001
X1	431.7	67.4	6.41	0.001 *
X2	–157.1	67.4	–2.33	0.067
X1X1	–38.1	80.2	-0.48	0.654
X2X2	–35.1	80.2	–0.44	0.680
X1X2	59.8	95.3	0.63	0.558
Parameters	Y2 Size (mm)
	Coefficient	Square Error	t -Value	p-Value
Constant	2.4667	0.0438	56.28	0.001
X1	–0.1689	0.0268	–6.29	0.001 *
X2	–0.0073	0.0268	–0.27	0.797
X1X1	0.0073	0.0319	0.23	0.828
X2X2	0.0073	0.0319	0.23	0.828
X1X2	–0.0075	0.0380	–0.20	0.851
Parameters	Y3 Sphericity (%)
	Coefficient	Square Error	t-Value	p-Value
Constant	98.300	0.241	407.54	0.001
X1	–0.369	0.148	–2.50	0.055
X2	–0.172	0.148	–1.16	0.298
X1X1	–1.388	0.176	–7.89	0.001 *
X2X2	–0.663	0.176	–3.77	0.013 *
X1X2	–0.025	0.209	–0.12	0.909

X₁: Heating temperature (°C), X₂: Heating time (min), * Significant at p < 0.05.