Fractional Factorial Designs in Minitab

Fractional factorial designs can be set up a couple of different ways in Minitab. If you'd like Minitab to pick out a 'good' fractional factorial design for you, enter the total number of factors you want to analyze in the Number of Factors box in the Create Factorial Design menu. Select Designs and choose the appropriate fraction (full factorial, 1/2 fraction, etc.) you would like to set up. Return to the main dialog box and, as usual, unselect the Randomized Runs box. Return to the main menu, click OK and your fractional factorial design will be selected for you. Minitab will print the alias structure of the preselected design in its Session window.

On the other hand, you may want to generate a design by specifying your own alias structure. As an example from class, suppose we wanted to alias D with the AB interaction (D=AB). Click on Create Factorial Design and choose the number of factors based on the number of runs in the experiment (i.e., for an 8-run experiment, select 3 factors even if 4 factors will eventually be selected); click the 2-level Factorial (specify generators) box. Click on the Designs box and select Full Factorial. Select Generators, type D=AB and click OK. Remember not to randomize the runs. Minitab will store the appropriate design in the worksheet and print the alias structure in the Session window.