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Interactions and interaction tables in Taguchi designs

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Taguchi designs are primarily intended to study main effects of factors. Occasionally, you might want to study some of the 2-way interactions. Some of the Taguchi designs (orthogonal arrays) let you study a limited number of 2-way interactions. This usually requires that you leave some columns out of the array by not assigning factors to them. Some of the array columns are confounded with interactions between other array columns. Confounding means that the factor effect is blended with the interaction effect, thus they cannot be assessed separately.

You can choose to have Minitab automatically assign factors to array columns in a way that avoids confounding. Or, if you know exactly what design you want and know the columns of the entire array that correspond to the design, you can assign factors to array columns yourself. Assigning factors to columns of the array does not change how the design looks in the worksheet. For example, if you assigned Factor A to Column 3 of the array and Factor B to Column 2 of the array, Factor A would still show up in Column 1 in the worksheet and Factor B would still show up in Column 2 in the worksheet.

What are interaction tables?

Interaction tables show confounded columns, which can help you assign factors to array columns. The columns and rows represent the column numbers of the Taguchi design (orthogonal array). Each table cell contains the interactions confounded for the two columns of the orthogonal array. The following are interaction tables for each array.

For example, the entry in cell (1, 2) is 3. This means that the interaction between columns 1 and 2 is confounded with column 3. Thus, if you assigned factors A, B, and C to columns 1, 2, and 3, you could not study the AB interaction independently of factor C. If you suspect that there is a substantial interaction between A and B, you should not assign any factors to column 3. Similarly, the column 1 and 3 interaction is confounded with column 2, and the column 2 and 3 interaction is confounded with column 1.

Interaction table for the L8(27) array

  1 2 3 4 5 6 7
1   3 2 5 4 7 6
2     1 6 7 4 5
3       7 6 5 4
4         1 2 3
5           3 2
6             1
Note

The L12 (211) array does not have an interaction table. It is a specially designed array, in that interactions are distributed more or less uniformly to all columns. There is also no linear graph for this array. It should not be used to analyze interactions. The advantage of this design is its capability to investigate 11 main effects, making it a highly recommended array.

Interaction table for the L16(2 15 ) array

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1   3 2 5 4 7 6 9 8 11 10 13 12 15 14
2     1 6 7 4 5 10 11 8 9 14 15 12 13
3       7 6 5 4 11 10 9 8 15 14 13 12
4         1 2 3 12 13 14 15 8 9 10 11
5           3 2 13 12 15 14 9 8 11 10
6             1 14 15 12 13 10 11 8 9
7               15 14 13 12 11 10 9 8
8                 1 2 3 4 5 6 7
9                   3 2 5 4 7 6
10                     1 6 7 4 5
11                       7 6 5 4
12                         1 2 3
13                           3 2
14                             1

Interaction table for the L27(313 ) array

  1 2 3 4 5 6 7 8 9 10 11 12 13
1   3 2 2 6 5 5 9 8 8 12 11 11
    4 4 3 7 7 6 10 10 9 13 13 12
2     1 1 8 9 10 5 6 7 5 6 7
      4 3 11 12 13 11 12 13 8 9 10
3       1 9 10 8 7 5 6 6 7 5
        2 13 11 12 12 13 11 10 8 9
4         10 8 9 6 7 5 7 5 6
          12 13 11 13 11 12 9 10 8
5           1 1 2 3 4 2 4 3
            7 6 11 13 12 8 10 9
6             1 4 2 3 3 2 4
              5 13 12 11 10 9 8
7               3 4 2 4 3 2
                12 11 13 9 8 10
8                 1 1 2 3 4
                  10 9 5 7 6
9                   1 4 2 3
                    8 7 6 5
10                     3 4 2
                      6 5 7
11                       1 1
                        13 12
12                         1
                          11

Interaction table for the L32(231 ) array

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1   3 2 5 4 7 6 9 8 11 10 13 12 15 14 17
2     1 6 7 4 5 10 11 8 9 14 15 12 13 18
3       7 6 5 4 11 10 9 8 15 14 13 12 19
4         1 2 3 12 13 14 15 8 9 10 11 20
5           3 2 13 12 15 14 9 8 11 1 0 21
6             1 14 15 12 13 10 11 8 9 22
7               15 14 13 12 11 10 9 8 23
8                 1 2 3 4 5 6 7 24
9                   3 2 5 4 7 6 25
10                     1 3 7 4 5 26
11                       7 6 5 4 27
12                         1 2 3 28
13                           3 2 29
14                             1 30
15                               31

Interaction table for the L32(231 ) array: continued

  17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
1 16 19 18 21 20 23 22 25 24 27 26 29 28 31 30
2 19 16 17 22 23 20 21 26 27 24 25 30 31 28 29
3 18 17 16 23 22 21 20 27 26 25 24 31 30 29 28
4 21 22 23 16 17 18 19 28 29 30 31 24 25 26 27
5 20 23 22 17 16 19 18 29 28 31 30 25 24 27 26
6 23 20 21 18 19 16 17 30 31 28 29 26 27 24 25
7 22 21 20 19 18 17 16 31 30 29 28 27 26 25 24
8 25 26 27 28 29 30 31 16 17 18 19 20 21 22 23
9 24 27 26 29 28 31 30 17 16 19 18 21 20 23 22
10 27 24 25 30 31 28 29 18 19 16 17 22 23 20 21
11 26 25 24 31 30 29 28 19 18 17 16 23 22 21 20
12 29 30 31 24 25 26 27 20 21 22 23 16 17 18 19
13 28 31 30 25 24 27 26 21 20 23 22 17 16 19 18
14 31 28 29 26 27 24 25 22 23 20 21 18 19 16 17
15 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
17   3 2 5 4 7 6 9 8 11 10 13 12 15 14
18     1 6 7 4 5 10 11 8 9 14 15 12 13
19       7 6 5 4 11 10 9 8 15 14 13 12
20         1 2 3 12 13 14 15 8 9 10 11
21           3 2 13 12 15 14 9 8 11 10
22             1 14 15 12 13 10 11 8 9
23               15 14 13 12 11 10 9 8
24                 1 2 3 4 5 6 7
25                   3 2 5 4 7 6
26                     1 6 7 4 5
27                       7 6 5 4
28                         1 2 3
29                           3 2
30                             1

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