Example of Create 2-Level Factorial Design (Default Generators)

A quality engineer wants to study the influence that six input variables (factors) have on the shrinkage of a plastic fastener of a toy. The engineer plans a pilot study to screen these six factors to determine which factors have the greatest influence on the response. The engineer is primarily interested in main effects and some 2-way interactions, so a resolution IV factorial design is appropriate. The engineer decides to generate a 16-run factorial design from Minitab's catalog of design experiments.

  1. Choose Stat > DOE > Factorial > Create Factorial Design.
  2. From Number of factors, select 6.
  3. Click Designs.
  4. Select the 1/4 fraction design.
  5. Click OK in each dialog box.

Interpret the results

The first table provides a summary of the design. With 6 factors, a full factorial design has 64 runs. Because of limited resources, the engineer selected the ¼ fraction with 16 runs. The ¼ fraction is a resolution IV design. The alias table shows that main effects are confounded with 3-way interactions, but not with any 2-way interaction or other main effects. Because 2-way interactions are confounded with each other, any significant interactions will need to be evaluated further to define their nature.

The Minitab worksheet below shows the settings for each factor for only the first 6 of the 16 experimental runs. The design was created using the default settings of −1 for low and 1 for high, although it is recommended that you enter actual settings for each level. The engineer uses the order that is shown in the RunOrder column to determine the settings for each run. For example, in the first run of the experiment, the settings are as follows: Factor A is high, Factor B is low, Factor C is low, Factor D is low, Factor E is high, and Factor F is low.

Note

Minitab randomizes the design by default, so when you create this design, the run order will not match the order in the worksheet shown below.

Fractional Factorial Design

Design Summary Factors: 6 Base Design: 6, 16 Resolution: IV Runs: 16 Replicates: 1 Fraction: 1/4 Blocks: 1 Center pts (total): 0

Design Generators: E = ABC, F = BCD

Defining Relation: I = ABCE = BCDF = ADEF

Alias Structure I + ABCE + ADEF + BCDF A + BCE + DEF + ABCDF B + ACE + CDF + ABDEF C + ABE + BDF + ACDEF D + AEF + BCF + ABCDE E + ABC + ADF + BCDEF F + ADE + BCD + ABCEF AB + CE + ACDF + BDEF AC + BE + ABDF + CDEF AD + EF + ABCF + BCDE AE + BC + DF + ABCDEF AF + DE + ABCD + BCEF BD + CF + ABEF + ACDE BF + CD + ABDE + ACEF ABD + ACF + BEF + CDE ABF + ACD + BDE + CEF
C1 C2 C3 C4 C5 C6 C7 C8 C9 C10
StdOrder RunOrder CenterPt Blocks A B C D E F
12 1 1 1 1 −1 −1 −1 1 −1
2 2 1 1 −1 1 1 −1 −1 −1
6 3 1 1 −1 −1 −1 −1 −1 −1
9 4 1 1 −1 −1 −1 1 −1 1
10 5 1 1 −1 −1 1 −1 1 1
1 6 1 1 1 1 −1 1 −1 −1
... ... ... ... ... ... ... ... ... ...
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