Critical values of the lenth method for unreplicated factorial designs

The Lenth method is an objective method for testing effects from unreplicat ed factorial designs and eliminates the subjectivity in using a half-normal plot. The Lenth statistics are computed for the factorial effects and comp ared to corresponding critical values. Since the distribution of the Lenth statistics is not mathematically tractable, we propose a simple simulation method to estimate the critical values. Confidence intervals for the estima ted critical values can also easily be obtained. Tables of critical values are provided for a large number of designs, and their use is demonstrated w ith data from three experiments. The proposed method can also be adapted to estimate critical values for other methods.