[R] LM intercept

[Peter Dalgaard]

Michael Just wrote:
> Great,
> Thanks,
> Michael
> 
> On Mon, Oct 13, 2008 at 3:56 PM, Rolf Turner <r.turner at auckland.ac.nz>wrote:
> 
>> On 14/10/2008, at 9:42 AM, Michael Just wrote:
>>
>>  What is the difference when including or not including the intercept when
>>> using lm()?
>>>
>>> x.noint <- lm(weight ~ group - 1))# omitting intercept
>>> x <- lm(weight ~ group))
>>>
>>> This has nothing to do with forcing the intercept to 0, correct?
>>>
>> On the contrary.  This is *exactly* what it means.


But if group is a factor, this removes the intercept _and_ uses the full 
set of indicator variables to represent the factor, so you end up with 
the same model, just parametrized differently.

-- 
    O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
   c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
  (*) \(*) -- University of Copenhagen   Denmark      Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)              FAX: (+45) 35327907