Specify the design for Create Definitive Screening Design

Stat > DOE > Screening > Create Screening Design > Designs

To specify the design, select the number of replicates and blocks.

Number of replicates

Select the number of replicates for the points. Replicates are multiple experimental runs with the same factor settings (levels). One replicate is equivalent to the base design, where you conduct each run once. With two replicates, you perform each run twice (in random order), and so on.

Adding replicates can help increase the precision of your model and increase the power to detect effects. To determine how many replicates to include in your design, consider the available resources and the purpose of your design. For example, in a screening design or in sequential experimentation you could begin with the base design (1 replicate) and then consider whether to add replicates after you analyze the data. For more information on replicates, go to Replicates and repeats in designed experiments.

Number of blocks

Select the number of blocks. If your design includes blocks, and the number of blocks equals the number of replicates, each replicate is a separate block. You can include multiple replicates in a block. Each block has the same number of replicates.

Blocks account for the differences that might occur between runs that are performed under different conditions. For example, an engineer designs an experiment to study welding and cannot collect all of the data on the same day. Weld quality is affected by several variables that change from day-to-day that the engineer cannot control, such as relative humidity. To account for these uncontrollable variables, the engineer groups the runs performed each day into separate blocks. The blocks account for the variation from the uncontrollable variables so that these effects are not confused with the effects of the factors the engineer wants to study. For more information on how Minitab assigns runs to blocks, go to What is a block?.

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