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# Re: st: What is the effect of centering on marginal effects?

 From John Antonakis To statalist@hsphsun2.harvard.edu Subject Re: st: What is the effect of centering on marginal effects? Date Fri, 03 Aug 2012 15:07:55 +0200

```Hi Kit:

```
Oops...I don't know what I was thinking there about the VIFs. In any case, as the two papers below show, the regression models are equivalent whether centering or not, and so are the marginal effects (of the FULL model).
```
Best,
J.
__________________________________________

Prof. John Antonakis
Faculty of Business and Economics
Department of Organizational Behavior
University of Lausanne
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Associate Editor
__________________________________________

On 03.08.2012 14:41, Christopher Baum wrote:
> <>
> On Aug 3, 2012, at 2:33 AM, John wrote:
>
>> I don't believe you are using the right vif.  Should it not be the
```
>> - -uncentered- option in vif for both regressions below? In this case the
```>> vifs are the same.
>
```
> Agreed, centering in VIF matters (my colleague David B. always recommends normalizing each column of X to unit length)
```> but that does not cause the VIFs to be equal:
>
> . estat vif, uncentered
>
>     Variable |       VIF       1/VIF
> -------------+----------------------
>       length |   1598.70    0.000626
>       weight |   1493.44    0.000670
>     c.length#|
>     c.weight |   1347.44    0.000742
>    intercept |   1180.62    0.000847
> -------------+----------------------
>     Mean VIF |   1405.05
>
>
>
> . estat vif, uncentered
>
>     Variable |       VIF       1/VIF
> -------------+----------------------
>     c_length |      9.71    0.102969
>     c_weight |      9.75    0.102591
>   c.c_length#|
>   c.c_weight |      1.94    0.516267
>    intercept |      1.91    0.522829
> -------------+----------------------
>     Mean VIF |      5.83
>
> Thanks for the references.
>
> Kit
>
>
```
> Kit Baum | Boston College Economics & DIW Berlin | http://ideas.repec.org/e/pba1.html > An Introduction to Stata Programming | http://www.stata-press.com/books/isp.html > An Introduction to Modern Econometrics Using Stata | http://www.stata-press.com/books/imeus.html
```>
>
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```