[R] logistic regression without intercept

Spencer Graves spencer.graves at pdf.com
Wed Aug 20 00:39:33 CEST 2003

Did you try the following:

 >>r <- glm(brain.cancer~epilepsy+other.cancer-1, c3,
 >>       family=binomial(link="logit") )

The construct "-1" on the right hand side of a formula means to exclude 
the intercept.  See, e.g., "model formulae" in the index to Modern 
Applied Statistics with S by Venables & Ripley.  I don't remember doing 
this with glm, but I've done it with lm.

hope this helps.  spencer graves

Ross Boylan wrote:
> I want to do a logistic regression without an intercept term.  This
> option is absent from glm, though present in some of the inner functions
> glm uses.  I gather glm is the standard way to do logistic regression in
> R.
> Hoping it would be passed in, I said
>>r <- glm(brain.cancer~epilepsy+other.cancer, c3, 
>>       family=binomial(link="logit"), intercept=FALSE)
> which produced
> Error in glm.control(...) : unused argument(s) (intercept ...)
> Is there an easy way to do this?  I suppose I could start hacking away
> at glm so it would take the argument and pass it on, but is it absent
> for a reason?
> Also, I noticed that S-Plus but not R has a glim routine that uses
> maximum likelihood.  What would be the equivalent?
> Thanks.
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