regression for the quadratic equation (Sy.122) is half
that of the linear equation (Sy.x2) and the coefficient of
determination R2 for the quadratic is much better than the
R2 for the linear equation.



 7500-



 7000- O




 6500-
 Rice
 kg/ha /


6000


5000


Nitrogen kg/ha


FIG.VI-8. Comparison of linear and quadratic response
 surfaces.