Why can't I detect curvature (nonlinearity) in DOE in JMP?

[#1]

In Minitab, if the factors in the DOE have center points, the curvature will be directly tested (i.e. nonlinearity, p<0.05 indicates that the curvature is significant), but there seems to be no such function in JMP?

[#2]

Hi @Xinghua,

The test for curvature in DoE is a frequent topic in the Community and has already some solutions. Please refer to the following posts and add-in :

Test For Curvature In 2 level full factorial with center points 

Another post on how to test for curvature in two-level factorial with center points, including discu... 

How to do a test for curvature in a DOE with JMP 

Pure Quadratic Curvature Test Add-In 

I think these references will help you,

[#3]

Many options in JMP to test for curvature with a DOE:

1. Choose a response surface design from the DOE > Classical menu.

2. Choose a Custom design and include quadratic (or higher) power effects.

3. Choose a Definitive Screening Design and include center points to estimate quadratic effects.

[#4]

Hi @Xinghua : Seems to me, the easiest thing to do would be to include the quadratic effect of any one of the factors in the model. The p-value for that effect is then the p-value for testing curvature.  Be warned though, whichever factor you used here may or may not be the factor that the quadratic effect is assigned to (it is confounded with the other potential quadratic effects). It's just a test to see if there is curvature present in at least one of the factors, so you will still need to augment the design to tease out which facture(s) is quadratic.

[#5]

While I haven't looked at the links provided by @Victor_G , and I agree with everything others have contributed to date, my first step, always, never fail, before any statistical test p, t, F, or otherwise, is to plot response vs. factor scatter plots. I hope at least one of those references encourages this approach. Your eye and process knowledge are the most sensitive 'detectors' of effects I've ever encountered. In 30 years of practice of DOE in an industrial setting I honestly can't recall one experiment we analyzed where a LOF test for curvature was 'significant' that didn't show up in scatter plots first.