Turn on suggestions

Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type.

Showing results for

- JMP User Community
- :
- Discussions
- :
- Re: Transformation of factor (in fit-model dialog) results in high VIF

- Subscribe to RSS Feed
- Mark Topic as New
- Mark Topic as Read
- Float this Topic for Current User
- Bookmark
- Subscribe
- Printer Friendly Page

Highlighted
##

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Get Direct Link
- Email to a Friend
- Report Inappropriate Content

Transformation of factor (in fit-model dialog) results in high VIF

Oct 10, 2016 10:57 PM
(4711 views)

Hello,

After execution of an experiment (CCD), I realized that it makes sense to log-transform one of the factors (I do it in the fit model dialog), which eventually gives a decent fit. However, the linear and square term have a high correlation then (VIF = 56). When manually transforming this factor, the VIF is low (VIF < 2). Can someone explain to me how this can happen and how I can avoid it?

Thanks!!!

Joachim

5 REPLIES 5

Highlighted
##

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Get Direct Link
- Email to a Friend
- Report Inappropriate Content

Re: Transformation of factor (in fit-model dialog) results in high VIF

I tried with my data but didn't see this behavior. Could you share the data and the models you ran?

Highlighted
##

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Get Direct Link
- Email to a Friend
- Report Inappropriate Content

Re: Transformation of factor (in fit-model dialog) results in high VIF

Attached now the file - should be self explanatory, just run the two models and check the VIFs. I am actually wondering, if it is related to the coding somehow. If using the "transform" option, I cannot code.

Thanks!

Highlighted
##

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Get Direct Link
- Email to a Friend
- Report Inappropriate Content

Re: Transformation of factor (in fit-model dialog) results in high VIF

Created:
Oct 13, 2016 8:34 AM
| Last Modified: Oct 18, 2016 9:21 PM
(4604 views)
| Posted in reply to message from joberi 10-13-2016

Yes, getting high VIFs is a result of the square term, Log(B)*log(B), not centered. (Center Polynomials is the default option when higher order terms are specified as model effects in Fit Model see Model Specification Options)

Somehow JMP won't automatically center the crossed terms on the transformed variables created temporarily within the Fit Model window.

Highlighted
##

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Get Direct Link
- Email to a Friend
- Report Inappropriate Content

Re: Transformation of factor (in fit-model dialog) results in high VIF

Hmm - ok - and what can I do now? Any workaround?

Thanks!

Highlighted
##

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Get Direct Link
- Email to a Friend
- Report Inappropriate Content

Re: Transformation of factor (in fit-model dialog) results in high VIF

*Add to Data Table* option to save them--done with two right mouse clicks.

Article Labels

There are no labels assigned to this post.