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Custom DOE - Issues with Continuous Factors, Runs only at Extreme Value

May 19, 2020 1:56 PM
(641 views)

I have a custom experiment I'm setting up.

I have 5 distinct surfaces I'm testing on. A, B, C, D, E.

I added a second factor, "load" as continuous from 5 to 15

I added a third factor "hold time" as 5 to 30

When I run "Make Design" Im surprised to see multiple runs of the same combination with all values at the extreme of the 2nd and 3rd factor. Is there a reason it doesn't have me test any intermediate combination?

Thanks in advance.

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- custom doe

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Re: Custom DOE - Issues with Continuous Factors, Runs only at Extreme Value

If you set the 2 additional factors to 2-levels (5, 15 and 5, 30), then the experiment will only provide treatment combinations at those 2-levels. If you want to test the factors at more than 2-levels, you must specify this when you add N Factors.

Level setting depends a lot on where you are in your study. 2-level designs are quite typical in early investigations (often called screening designs). The levels are chosen far enough apart to have a wide inference space. Essentially you are increasing the chance of seeing a factor effect, of course, this is done for all of the factors to mitigate bias. 2-level designs will allow for first order model development as well as the ability to estimate interactions provided the design has enough resolution. As your study approaches "optimal", then typically some sort of RSM is used often with more than 3-levels for factors thereby being able to estimate complex non-linear relationships.

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Re: Custom DOE - Issues with Continuous Factors, Runs only at Extreme Value

A slightly different way to look at this: JMP will choose the design according to the model that you want to estimate. If you have only main effects, then you only need 2 levels to estimate those straight line relationships. If you require curvature (like squared terms), then you will get 3 levels for the factors.This is where you get efficiency: only perform the levels required to estimate the desired models.

Dan Obermiller

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Re: Custom DOE - Issues with Continuous Factors, Runs only at Extreme Value

If you want to test the factors at more than 2-levels, you must specify this when you add N Factors.

Do you mean manually adding additional level at the mid point? So instead of 2-level, I should choose 3-level?

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Re: Custom DOE - Issues with Continuous Factors, Runs only at Extreme Value

Created:
May 20, 2020 9:20 AM
| Last Modified: May 20, 2020 10:05 AM
(587 views)
| Posted in reply to message from csf 05-20-2020

As Dan suggests, you can add quadratic terms to the model you want to estimate, or you can add Discrete Numeric 3-level as in attached pic.

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Re: Custom DOE - Issues with Continuous Factors, Runs only at Extreme Value

Created:
May 20, 2020 9:23 AM
| Last Modified: May 20, 2020 10:04 AM
(585 views)
| Posted in reply to message from statman 05-20-2020

Screen shot of adding "powers"..2nd.

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