“…In comparing the prediction capabilities of some response surface designs , the Variance Dispersion Graph (VDG) proposed by Giovannitti-Jensen and Myers (1989) has been used; see, for example, Borkowski(1995), Li, Liang, Borror, Anderson-Cook and Montgomery (2009). Ukaegbu and Chigbu (2015) used the VDG and Fraction of Design Space (FDS) to compare the prediction variances of partially replicated ccd in cuboidal region and conclude that the replicated star is economically feasible than the replicated cube. VDG does not provide enough information on the effect of design on the prediction variance, hence, Khuri, Kim and Um (1996) proposed a method for describing the distribution of the predicted variances on a given sphere in terms of its quantiles.…”