In partial summary, the following values have been
calculated to help determine the significance of the
equation:

 R2 = 0.920
 tI = 3.459 (2.5%)
 t2 = 2.0160 (10%)
 Fc = 17.2114 (2.5%)

In general, these values and levels of significance are
high, which indicates that the response surface calculated
is very representative of the real biological response
demonstrated by the data. For this reason, it is probably
not necessary to make other calculations to study the
significance of the response surface. Nevertheless, in
order to demonstrate the use of other analyses, the same
equation will be used.

Linear versus Quadratic Surface

 In some cases, it may be logical to wonder if a
linear response better fits the data than a curvilinear
response. From the same rice data (Table VI-2), a linear
equation of the form Y = a + bN can be calculated. The
value of b is:

 b = Exly / Ex12
 = 4.875/9.0
 = 0.5416

Using the mean value of Y and X, the value of a is:

 a = Y b(Xl)
 = 6.333 0.5416(1.5)
 = 5.5206

The linear equation is:

 Y = 5.5206 + 0.5416 N

Note that the b in the linear equation is different from
the value of bl in the quadratic equation.
 The "goodness of fit" of the linear equation can be
evaluated by