# Specify the options for Create 2-Level Split-Plot Design

Stat > DOE > Factorial > Create Factorial Design > Options

## Fraction

If the design is a fractional factorial, then you can select which fraction to use. You can estimate the same terms with any fraction. Usually, you specify a different fraction from the default because one or more combinations of factor levels that are in the principal fraction are impractical to run. For example, the principal fraction always includes the run where all of the factors are at their high setting. The other fractions do not. If setting all of the factors at their high levels is expensive or difficult, you can change the fraction number. For more information on selecting a fraction, go to Factorial and fractional factorial designs.

• Use principal fraction: The principal fraction is the fraction where all of the signs for the design generators are positive.
• Use fraction number: The fraction number distinguishes the runs in the design from another set of runs that form the same size fraction. The possible fraction numbers depend on the fraction of the design. For example, if the design is a ¼ fraction, then the possible fraction numbers are 1, 2, 3, and 4. In Minitab, the principal fraction is the highest integer of the possible fraction numbers. For example, if the design is a 1/8 fraction, then the principal fraction is 8. In the case of the 1/8 fraction, enter an integer from 1 − 7 to get a different fraction.

## Randomize runs

Select whether Minitab randomizes the run order within each whole plot. Also, the order of the whole plots is randomized. Randomization reduces the chances of confounding between the effects of factors in your study with the effects of factors that are not in the study, particularly effects that are time-dependent.

Base for random data generator
Specify a base for the random data generator so that you can obtain the same random order when you create another design. When you enter the same base, the run order is the same.

After the design is in the worksheet, you can change how you view the design and re-randomize the design. To view a design in standard order or random order, use Display Design. To randomize or re-randomize a design, use Modify Design. For more information, go to Overview for Display Design and Modify Design.