[R-sig-eco] Standardising and transformation of explanatory/independent/predictor variables for multiple regression analysis

[Scott Foster]

Hi again Sam,

I think that you have it.  Extreme values will have more influence, due to their placement in covariate space.  This is often countered with 
transformation (of the covariates) but I tend to think that altering your data for the sake of the model is the wrong way around.  Nevertheless, it 
can be effective.  Especially when there is a reason (from the application) to do so.  Using other methods may also help, without the need to transform.

Note that this is not the same issue as transforming the outcomes (responses).  There I would try my hardest not to transform at all -- transformation 
can do funny things to the statistical properties of the outcomes (and it is those statistical properties that are of direct interest).

Good luck,

Scott

On 05/09/14 01:12, SamiC wrote:
> Thanks Scott,
>
> That does help to clarify things.
>
> So if a covariate is highly skewed, extreme values will be more influential.
> And this can be reduced through a transformation (which can be justified) or
> through other techniques (e.g. bootstrapping).
>
> Cheers
>
> Sam
>
>
>
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-- 
Scott Foster
CSIRO
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