Comparison of Rotatable Designs for Regression on Balls

Abstract Designs for quadratic and cubic regression are considered when the possible choices of the controlable variable are points x =( x 1 , x 2 ,…, x q ) in the q -dimensional. Full of radius R , B q ( R ) ={ x : Σ 4 i x 2 i ⩽ R 2 }. The designs that are optimum among rotatable designs with respect to the D -, A -, and E -optimality criteria are compared in their performance relative to these and other criteria, including extrapolation. Additionally, the performance of a design optimum for one value of R , when it is implemented for a different value of R , is investigated. Some of the results are developed algebraically; others, numerically. For example, in quadratic regression the A -optimum design appears to be fairly robust in its efficiency, under variation of criterion.