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I can not get the result of the main effect when I choose the 2nd interaction with mixture factors.

Dear All,

 

Here's our homepage's split plot experiment example.

 

https://www.jmp.com/support/help/14/split-plot-experiment.shtml

 

And when I did it, the pop-up window appeared.

 

 

 

 

 

 

 

 

 

 

And the page I said mentioned above that " Click OK to dismiss the informative message ".

 

I can not understand why the main effects are removed for non-mixture factors. Could anyone tell me why?

 

Thanks in advance.

Re: Why I cannot get the result of main effect when I choose 2nd interaction with mixture factors?

This result is about a constraint and the parameterization of the linear model.

The mixture factors (A, B, C) are constrained to sum to one. (A+B+C=1) That constraint is the reason that the intercept (I) is removed. Without a constraint, a pure blend of A alone would be modeled as Y=bA+I. With the constraint, the model is Y=b'A.The Y is the same and the Y prediction is the same but the parameter b and b' are different. So is there interpretation. The average response is implicitly modelled already by the 'main effect' terms. Adding an explicit term for the intercept would cause a singularity during the estimation of the model parameters.

Similarly, the cross terms that you added implicitly represent the main effect of the non-mixture factor (D), so the explicitly term for it must be removed.

Re: Why I cannot get the result of main effect when I choose 2nd interaction with mixture factors?

Thanks Mark.

 

I can understand because of the constraint there sholud be removed main effect terms.
But what canI do if I want to get the estimates of main effect terms?

 

In this case(Split plot design via custom design) when I have adjusted 2nd interaction, then runs are 21.

After that, I click the main effect of two extrusion rate and temperature by force, then the rus are 20 less than above experiment.

 

My queston is...

 

One. When I want to see the main factors' effect with mixture factors, can I adjust the main effects by force after applying 2nd interaction? Of course when I apply 2nd interaction, the main effect terms are removed already.

 

2. If #1 is right(adjust main effects after applying 2nd interactions) why the runs are less than 21?

 

Best