[R] How to exclude insignificant intercepts using "step" function

[Dieter Menne]

David Winsemius wrote:
> 
> 
> On Jun 23, 2009, at 3:08 AM, Chris Friedl wrote:
> The point is that in very few applications can one legitimately  
> "exclude" an intercept. In this situation (stepwise regression) I am  
> able to think of a way to make the intercept just another covariate,  
> but I see theoretic objects with that approach. Of course there are  
> problems with stepwise regression as well.
> 

I agree with David's warning. You should have a-priori knowledge that the
intercept is zero, not one derived from the significance. For example, when
your have hill-races (from MASS), where you know that for 0 meter (sorry,
inches) you need 0 seconds; or from growth curves of artificial bone
material, where  by definition at t=0 you start with zero bone.

Dieter


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