Alternative Axial Distances for Spherical Regions of Central Composite Designs

  • Linus Ifeanyi Onyishi Department of Mathematics and Statistics, Federal Polytechnic, Nasarawa, Nasarawa State, Nigeria
  • F. C. Eze Department of Statistics, Nnamdi-Azikiwe University, Awka, Nigeria
Keywords: spherical design, optimality criteria, axial distances, central composite design, Pythagorean means


Alternatives to the existing axial distances of the Central Composite Design (CCD) in spherical design using three axial distances were studied. The aim of this study is to determine a better alternative to already existing axial distances whose prediction properties are more stable in the spherical design regions. Using the concepts of the three Pythagorean means, the arithmetic, harmonic and geometric axial distances for spherical regions were developed. The performances of the alternative axial distances were compared with the existing ones using the D and G optimality criteria. The study shows that the alternative axial distances are better using the D and G optimality criteria.