Choosing a response surface design
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Before you use Minitab, you need to determine what design is most appropriate for your experiment. Choosing your design correctly will ensure that the response surface is fit in the most efficient manner. Minitab provides central composite and Box-Behnken designs. When choosing a design you need to

·    identify the number of factors that are of interest.

·    determine the number of runs you can perform.

·    ensure adequate coverage of the experimental region of interest

·    determine the impact that other considerations (such as cost, time, or the availability of facilities) have on your choice of a design.

Depending on your problem, there are other considerations that make a design desirable. You need to choose a design that shows consistent performance in the criteria that you consider important, such as the ability to

·    increase the order of the design sequentially.

·    perform the experiment in orthogonal blocks. Orthogonally blocked designs allow for model terms and block effects to be estimated independently and minimize the variation in the estimated coefficients.

·    rotate the design. Rotatable designs provide the desirable property of constant prediction variance at all points that are equidistant from the design center, thus improving the quality of the prediction.

·    detect model lack of fit.