DoE CCD

[#1]

Hello,

I created a series of experiments using DoE (effect surface design). After conducting the experiments, I obtained a Pareto chart at a significance level of 0.02, in which a reference line (blue line) is drawn. I would like to know what value my reference line is? Can I have the value calculated?

Thank you very much

Greetings

[#2]

Hi @ZE : Welcome to the forum. It is the critical value from the t distribution. It depends on alpha (0.05 by default) and the error degrees of freedom (from the ANOVA table).  In JMP they are calculated (+/-), respectively, as shown below (where df = Error DF from ANOVA table).

-t Quantile( 0.975, df ), t Quantile( 0.975, df )

 This is explained in the Sorted Estimates help:

Sorted Estimates (jmp.com)

[#3]

Hi MRB3855

Thanks for the quick reply. I had 15 runs and set the alpha value to 0.02. Is there no way in the software to give me the value for the blue line (reference line)? I would like to create a diagram for my report and need the value for this line. In Minitab, I was given a value of 3.36 for the blue reference line.

Many thanks in advance.

[#4]

Hi @ZE Here ya go.

t Quantile( 0.01, 5 ) and  t Quantile( 0.99, 5 )

In general, t Quantile (alpha/2, Error df)  and t Quantile ( 1-alpha/2, Error df)

[#5]

Hi @MRB3855

I appreciate that. The main problem is that I don't get the same value as with Minitab (critical t-value = 3.36) and that makes me a bit unsure. I have 3 factors that have changed in three levels and occur 5 times each in the trials (15). So I have 14 DF and when I read the t-value at the 0.02 and 14 DF significance levels, I get 2.62.

[#6]

Hi @ZE : You have 15 total runs?  If so, you have 9 terms (3 main effects, 3 quadratic effects, and 3 pairwise interactions) in your model and that leaves only 5 df for Error. So 3.36 is correct; you have 14 df Total, but it is the Error df that matters. 

Or am I misunderstanding?

[#7]

Hi @MRB3855 

no, you're right. i'm sorry, i made a small logical mistake and always calculated with the total degree of freedom.