QPRC 2016

The second-order model and the location of the stationary point

Antonio F. B. Costa
The State University of São Paulo - Brazil

The second-order models with main effects (x), quadratic terms (x2) and first-order interactions (xy) accommodate well most of the systems containing curvature,  but not all of them. In some cases, with these standard models (even with R2 > 0.80) we obtain huge confidence regions on location of the stationary point.   If x2y terms can also be tested, then the selected second-order model might lead to a smaller confidence region. The point we address in this study is the mathematical  development to obtain the confidence region when the selected model has x2y terms.