To begin, select DOE > Screening Design, or click the Screening Design button on the JMP Starter DOE page. Then, see the following sections for each step to create a screening design:
Display and Modify Design, if you choose a standard design from the Design Table
Design Generation, if you choose to generate a main effects screening design
Entering Responses
Tip: To quickly enter multiple responses, click the Number of Responses button and enter the number of responses you want.
The Minimize goal supports an objective of having the smallest value be the most desirable, such as when the response is impurity or defects.
The Match Target goal supports the objective when the best value for a response is a specific target value, such as dimensions of a manufactured part. The default target value is assumed to be midway between the lower and upper limits.
When computing overall desirability, JMP uses the value you enter as the importance weight (step 4 in Entering Responses) to weight each response. If there is only one response, then specifying importance is unnecessary. With two responses you can give greater weight to one response by assigning it a higher importance value.
1.
To enter a continuous factor, click the Continuous button. To enter a Discrete Numeric or a Categorical factor, select the appropriate number of levels for the factor from the list.
2.
To enter several of one type of factor, enter the number of factors in the box next to Add N Factors. Then select the type of factor for which you want to add the specified number of factors.
Entering Factors
Choosing a Type of Screening Design
A regular fractional factorial design also has a sample size that is a power of two. If k is the number of factors, the number of runs in a regular fractional factorial design is 2k – p where p < k. The fraction of the full factorial is 2-p. Like the full factorial, regular fractional factorial designs are orthogonal.
The trade-off in screening designs is between the number of runs and the resolution of the design. If price is no object, you can run several replicates of all possible combinations of m factor levels. This provides a good estimate of everything, including interaction effects to the mth degree. But because running experiments costs time and money, you typically only run a fraction of all possible levels. This causes some of the higher-order effects in a model to become nonestimable. An effect is nonestimable when it is confounded with another effect, meaning that the effects can not be distinguished from each other. In fact, fractional factorials are designed by deciding in advance which interaction effects are confounded with the other interaction effects.
Experiments can therefore be classified by resolution number into three groups:
Resolution 5 means there is no confounding between main effects, between two-factor interactions, or between main effects and two-factor interactions.
A minimum aberration design is one in which there are a minimum number of confoundings for a given resolution. For DOE experts, the minimum aberration design of a given resolution minimizes the number of words in the defining relation that are of minimum length.
The figure on the right in Representation of Full Factorial (Left) and Two-Level Fractional Factorial (Right) Designs is a geometric representation of a two-level fractional factorial design with three factors.
In cases of effect sparsity, a stepwise regression approach can allow for removing some insignificant main effects while adding highly significant and only somewhat correlated two-factor interactions. The Screening platform in JMP, Analyze > Modeling > Screening, is a streamlined approach for looking at sparse data. This platform can accept multiple responses and multiple factors, then automatically fits a two-level design and shows significant effects with plots and statistics. See Analyzing Screening Data for details.
Cotter designs are easy to set up. For k factors, there are 2k + 2 runs. The design is similar to the “vary one factor at a time” approach many books call inefficient and naive.
A Cotter design begins with a run having all factors at their high level. Then follow k runs each with one factor in turn at its low level, and the others high. The next run sets all factors at their low level and sequences through k more runs with one factor high and the rest low. This completes the Cotter design, subject to randomizing the runs.
When you use JMP to generate a Cotter design, the design also includes a set of extra columns to use as regressors. These are of the form factorOdd and factorEven where factor is a factor name. They are constructed by adding up all the odd and even interaction terms for each factor. For example, if you have three factors, A, B, and C:
1.
Immediately after entering responses and factors (and before clicking Continue), click the red triangle icon in the Screening Design title bar.
2.
Deselect Suppress Cotter Designs. (The option is initially selected.)
Changing the setting via the red triangle menu applies only to the current design. To alter the setting for all screening designs:
1.
Select File > Preferences.
2.
Click the Platforms icon.
3.
Click DOE to highlight it.
4.
Uncheck the box beside Suppress Cotter Designs.
Display and Modify Options
Generating Rules and Aliasing of Effects Panel
For example, a full factorial with five factors requires 25 = 32 runs. Eight runs can only accommodate a full factorial with three two-level factors. It is necessary to construct the two additional factors in terms of the first three factors.
In the example above, the values for Temperature are the product of the values for Feed Rate and Concentration. This means that you can’t tell the difference of the effect of Temperature and the synergistic (interactive) effect of Feed Rate and Concentration.
In the example shown in Generating Rules and Aliasing of Effects Panel, all the main effects are confounded with two-factor interactions. This is an example of a resolution-three design.
2.
Select Show Confounding Pattern (Show Confounding Patterns).
Show Confounding Patterns
Enter Order of Confounding in Text Edit Box
4.
The Third Level Alias for the Five-Factor Reactor Example shows the third order aliasing for the five-factor reactor example. The effect names begin with C (Constant) and are shown by their order number in the design. Thus, Temperature appears as “4”, with second order aliasing as “1 5” (Feed Rate and Concentration), and third order confounding as “1 2 3” (Feed Rate, Catalyst, and Stir Rate).
The Third Level Alias for the Five-Factor Reactor Example
In the Coded Design panel, each row represents a run. Plus signs designate high levels and minus signs represent low levels. As shown in Default Coded Designs, rows for the first three columns of the coded design, which represent Feed Rate, Catalyst, and Stir Rate are all combinations of high and low values (a full factorial design). The fourth column (Temperature) of the coded design is the element-by-element product of the first three columns. Similarly, the last column (Concentration) is the product of the second and third columns.
Default Coded Designs
In the Change Generating Rules panel, changing the check marks and clicking Apply changes the coded design; it changes the choice of different fractional factorial designs for a given number of factors. The Coded Design table in Default Coded Designs shows how the last two columns are constructed in terms of the first three columns. The check marks in the Change Generating Rules table shown in Modified Coded Designs and Generating Rules for Temperature now show it is a function of Feed Rate, and Catalyst. The check marks for Concentration show it is a function of Feed Rate and Stir Rate.
If you check the options as shown in Modified Coded Designs and Generating Rules and click Apply, the Coded Design panel changes. The first three columns of the coded design remain a full factorial for the first three factors (Feed Rate, Catalyst, and Stir Rate). Temperature is now the product of Feed Rate and Catalyst, so the fourth column of the coded design is the element by element product of the first two columns. Concentration is a function of Feed Rate and Stir Rate.
Modified Coded Designs and Generating Rules
Use the Output Options panel to specify how you want the output data table to appear. When you have finished, click Make Table to construct a data table for the design. Select the Output Options shows the Output Options panel for a standard design. For a main effects screening design, only Run Order is available.
Select the Output Options
Keep the Same The rows (runs) in the output table appear as they do in the Coded Design panel.
Sort Left to Right The rows (runs) in the output table appear sorted from left to right.
Randomize The rows (runs) in the output table appear in a random order.
Sort Right to Left The rows (runs) in the output table appear sorted from right to left.
Randomize within Blocks The rows (runs) in the output table appear in random order within the blocks you specify.
Click Make Table to create a data table that contains the runs for your experiment. In the table, the high and low values you specified are displayed for each run.
The Design Data Table
The name of the table is the design type that generated it. Run the Screening script to screen for active effects. The column called Pattern shows the pattern of low values denoted “–” and high values denoted “+”. Pattern is especially useful as a label variable in plots.