Term Coef SE Coef T P Constant 63.1787 0.12676 498.418 0.000 X1 -5.5239 0.08963 -61.629 0.00 X2 -2.5246 0.08963 -28.166 0.000 X3 -1.8900 0.08963 -21.086 0.000 X4 2.1601 0.08963 24.100 0.000 X1* X1 -1.6905 0.11857 -14.257 0.000 X2* X2 -1.3719 0.11857 -11.570 0.000 X3* X3 -0.8366 0.11857 -7.056 0.000 X4* X4 -1.1084 0.11857 -9.348 0.000 X1* X2 -0.0290 0.15525 -0.187 0.854 X1* X3 0.9434 0.15525 6.077 0.000 X1* X4 -6.4986 0.15525 -41.860 0.000 X2* X3 -0.7445 0.15525 -4.796 0.000 X2* X4 5.5148 0.15525 35.523 0.000 X3* X4 -1.0086 0.15525 -6.497 0.000

Table 3: Regression analysis for citric acid production.