The best plane through data

Conclusions

As can be seen from Table 1, the two trend surfaces give considerably different values. Our data were chosen not to fit any one plane and this is reflected in both of the trend surfaces. The program has been run with different data, and as the data tend toward a plane both trend surfaces become nearly identical as one would expect.

We conclude that the type of plane to use for trend-surface analysis does indeed depend on the hypotheses of the fitting technique.