R help - Feb 2004 - display functions in groupedData and lme

I'm trying to set up a mixed model to solve using lme.  It will have 3 
fixed effects, two random effects and two interaction terms. 

I've been reading Pinheiro's and Bates's book on the nmle library,
but
find the part about display functions to be unclear.  When creating a 
groupedData object from a data.frame, you need to enter a function of the 
form: response ~primary|grouping

Does this display function serve any purpose later on when specifying the 
model in the call to lme?  If so, how would I include more terms in 
primary or grouping (I tried primary1+primary2+... as per one post in the 
archives, but it didn't work).  If not, is it just for purposes of 
displaying the data?

Thanks much,
Scott Rifkin

Dear Scott,

I believe that normally the display formula is just used to construct 
graphs of the data, although when a grouped-data object is passed in the 
data argument to lme(), the grouping structure can be obtained from the 
object and need not be specified explicitly. As well, it is possible to 
specify additional "outer" and "inner" covariates beyond the
principal
covariate given in the display formula, and these can be used in graphs of 
the data. All this is described, if I remember right, in the section on 
grouped-data objects in Pinheiro and Bates.

I hope that this helps,
  John

At 07:50 PM 2/6/2004 -0500, Scott Rifkin wrote:
>I'm trying to set up a mixed model to solve using lme.  It will have 3
>fixed effects, two random effects and two interaction terms.
>
>I've been reading Pinheiro's and Bates's book on the nmle
library, but
>find the part about display functions to be unclear.  When creating a
>groupedData object from a data.frame, you need to enter a function of the
>form: response ~primary|grouping
>
>Does this display function serve any purpose later on when specifying the
>model in the call to lme?  If so, how would I include more terms in
>primary or grouping (I tried primary1+primary2+... as per one post in the
>archives, but it didn't work).  If not, is it just for purposes of
>displaying the data?
-----------------------------------------------------
John Fox
Department of Sociology
McMaster University
Hamilton, Ontario, Canada L8S 4M4
email: jfox at mcmaster.ca
phone: 905-525-9140x23604
web: www.socsci.mcmaster.ca/jfox