[R] fitted values in LMER for the fixed-effects only

[Anouk Simard]

Hi,

I would like to extract the fitted values from a model using LMER but 
only for the fix portion of the model and not for the fix and random 
portion (e.g it is the procedure outpm or outp in SAS). I am aware of 
the procedure fitted() but I not sure it give the fitted values both for 
the fixed and random or only the fixed. I looked in the r help and the r 
list and I haven’t not found much details about it excepted this 
comments from Douglas Bates in January 2006 :

“Would it help if there were an option in the fitted method to allow for 
fixed-effects only versus fixed- and random-effects? As you say, because 
lmer models do not need to be hierarchical it is not obvious what it 
would mean to include some but not all of the random effects terms in 
the "fitted values". However, it is easy and unambiguous to define 
fitted values for the fixed-effects only.

Up until a few days ago there was an option to do this but then I 
changed the calculation of the fitted values in an attempt to clean up 
the code. The calculation of the level = 0 fitted values in the new 
representation of the fitted model is quite easy. It is

fm1 at X %*% fixef(fm1)”

I tried the last formula, but I want to confirm that this is still the 
proper and best way to get fitted values for the fix effects using lmer.

Thanks