A Note on cost-effective asymmetrical rotatable designs

Response surface designs are very commonly used in process and product optimization studies. It is used in situations where several input variables potentially influence some performance measure or quality characteristic of a process. But majority of such studies are based on symmetric rotatable designs. Rotatable designs that are asymmetric are useful in situations where it is desirable to maintain the rotatability but it is difficult or infeasible to have the same number of levels for all the factors. Randomization in run order is a technique commonly employed by the users of response surface designs to avoid biases in the estimates of the effects of interest which might result from a time trend. But, randomization can induce a large number of changes in factor levels and thus make experimentation expensive and difficult. Here, a method to obtain experimentation orders with the desired properties for asymmetric response surface designs has been discussed.