Test of adequacy

A further test of adequacy is the plot of observed vs. fitted values which is shown in Figure 5. The points generally fall along the reference line for a perfect fit. Further, the deviations from the reference line appear to be randomly distributed. 

Here, we want to emphasize that one is able to calculate the fraction of the experimental error only if replicate measurements (at least at one point x ) have been taken. It is then possible to compare model and experimental errors and to test the sources of residual errors. Then, in addition to the GOF test one can perform the test of lack of fit, LOF, and the test of adequacy, ADE, (commonly used in experimental design). In the lack of fit test the model error is tested against the experimental error and in the adequacy test the residual error is compared with the experimental error. 

In that case the test of adequacy is performed with a y2-test ... 

If interpolation of the values of the target variable y is necessary, for example to find better estimates of the model error (for tests of adequacy), the variables, z, in Eq. 3-9 must be retransformed using Eqs. 3-6 to 3-8. 

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