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Sep 19, 2017 1:55 AM
(726 views)

Hi...

I am analysing a DOE with centerpoint runs, since we want to know if there are significant quadratic effect.

known info:

- 4 factors are involved with 4 replications in the center point
- the factorial portion of the design is a full-factorial that includes 2^4=16 runs
- so, the total number of runs of your design is 20
- each run produced 20 values (readings) a total of 20 x 20 = 400 readings

In the analysis, only 1 quadratic effect has P-value, as far as i know, as far as i have enough number of runs to estimate all the main and 2nd degree effects (2-way interactions and quadratic), JMP should be able to compute for all the needed p-values. But why am i getting this result? See attached

Please correct my understanding if im wrong, and thanks to help figure out the problem with my data

2 REPLIES

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Sep 19, 2017 6:35 AM
(712 views)

Your design does not support the estimation of the full quadratic model. It is a two-level design, which supports only the estimation of the first order model. The center points provide a third level but they can only be used for either a lack of fit test (LOF) or the estimation of one arbitrarily selected quadratic effect. The data are incapable of uniquely determining the factor attributable to the non-linear effect.

I would deleted the quadratic terms for all the non-linear effects and fit the model. Is LOF significant? If so, then I would augment the design after adding the quadratic terms to the model. If not, then there is no significant non-linearity to account for, so your first order model is sufficient.

Learn it once, use it forever!

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Sep 19, 2017 11:30 AM
(697 views)