Dear Thuy,

For the second question: to my knowledge, No, you have to use the same alpha for all the factors.

Kind regards

Dear Aicha,

Thank you for your input. Meanwhile I did some research and I found out that the factors do not have to have the same alpha level. It was mentioned in a webinar by StatEase.

Dear Thuy,

That's good to know. However, when I tried to use different alphas in the software I couldn't.

Please could you share with me how you did it?

Dear Aicha,

you can build the design first and then manually set the factor levels of the axial points to the low and high level (or any other level) in the design overview.

For reference, this is the webinar where I found the information. Unfortunately, I cannot post a link in here, but search for "Keys to Building the Perfect Response Surface Design StatEase" on YouTube. It is mentioned it minute 25:20.

Dear Thuy,

Thank you for the reference. Actually, in that minute they were talking about changing alpha when it goes negative. I agree with that.

However, it changes to all factors at the same time, I couldn't use different alphas to different factors. ( I am working with design expert 13)

Dear Aicha

I am using the same version of the software. I built the design with the same alpha for all factors. Then press the finish button and it will take you to the design overview, where all of your runs are laid out. It is the same overview, where you can enter the responses. Here, it should be possible to edit the factor levels according to your needs (just overwrite the values).

Dear Thuy,

That's a smart trick. Thank you for sharing it.