In this work, the performances of the partially replicated-cube and -star (axial) portions of orthogonal central composite designs (CCD) in spherical regions are studied. The replication of the cube and star portions of the CCD without replicating the centre point for k = 3, 4, 5 and 6 number of factors is the main focus. The interest is to evaluate the performance of the CCD with respect to the stability, small prediction variance and prediction capability, when replication is at other points away from the centre of the design. The variance dispersion graphs and fraction of design space plots are the two graphical techniques used while Dand G-efficiencies are the single-value optimality criteria utilized in the assessment. The results show that replicating the star portions of the CCD considerably reduces the prediction variance, thereby improving the G-efficiency in the spherical region and, therefore, recommended for prediction with precision and with smaller number of runs than replicating the cube.

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