Using quantile plots of the prediction variance for comparing designs for a constrained mixture region: an application involving a fertilizer experiment

Vining and co-workers have used plots of the prediction variance trace (PVT ) along the so-called prediction rays to compare mixture designs in a const rained region R. In the present paper, we propose a method for describing t he distribution of the prediction variance within the region R by using qua ntile plots. More comprehensive comparisons between mixture designs are pos sible through the proposed plots than with the PVT plots. The utility of th e quantile plots is illustrated with a four-component fertilizer experiment that was initiated in Sao Paulo, Brazil.