Transformation of factor (in fit-model dialog) results in high VIF<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />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
Re: Transformation of factor (in fit-model dialog) results in high VIFThe work around is just like what you already did: saving the transformed columns to your data table before you specify your models. Are you using this feature Transform Columns ? It lets you quickly create new columns (e.g.,log) in Fit Model launch window (in the column list pane) and then use Add to Data Table option to save them--done with two right mouse clicks.
Re: Transformation of factor (in fit-model dialog) results in high VIFHmm - ok - and what can I do now? Any workaround?
Thanks!
Re: Transformation of factor (in fit-model dialog) results in high VIFYes, 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.
Re: Transformation of factor (in fit-model dialog) results in high VIFAttached 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!
Re: Transformation of factor (in fit-model dialog) results in high VIFI tried with my data but didn't see this behavior. Could you share the data and the models you ran?
