Custom Factorial Designs in Minitab To create runs for custom fractional factorial designs, you select Stat>DOE>Create Factorial Design. On the main screen, you click on "2-level factorial, specify generators" and choose k-p (not k) as the number of factors. Hit the Designs key and select the Full Factorial Design; click on Generators. In the Generators screen, choose which interactions of the original k-p factors you would like to alias with each of the p remaining main effects. E.g., for a 1/16 fraction of a 2^7, you would enter D=AB E=AC F=BC G=ABC. Make sure not to randomize runs and you'll get a customized design in all k factors.