Second Order Slope Rotatable Designs under Tri-diagonal Correlation Structure of Errors Using a Pair of Incomplete Block Designs
B. Sulochana *
Department of Statistics, Acharya Nagarjuna University, Guntur-522510, India.
B. Re. Victorbabu
Department of Statistics, Acharya Nagarjuna University, Guntur-522510, India.
*Author to whom correspondence should be addressed.
Abstract
Box and Hunter [1] introduced the concept of rotatability for response surface designs. The concept of slope-rotatability was introduced by Hader and Park [2] as an analogous to rotatability property, which is an important design criterion for response surface design. Slope-rotatable design is that of which the variance of partial derivative is a function of distance from the design (d). Recently, a few measures of slope-rotatability for a given response surface design was introduced. In this paper, a new method of slope rotatability for second order response surface designs under tri-diagonal correlation structure of errors using a pair of symmetrical unequal block arrangements with two unequal block sizes is studied. Further, a study on the dependence of variance function of the second order response surface at different design points for different values of tri-diagonal correlation coefficient ρ which lies between -0.9 to 0.9 and the distance from centre (d) is suggested.
Keywords: Response surface designs, slope rotatability, tri-diagonal correlation errors, symmetrical unequal block arrangements with two unequal block sizes.