[R] multiple nesting levels in GEE

[Aurelie.Cohas@univ-lyon1.fr]

 Hello,

I'm actually trying to fit a gee model with 2 nesting levels since I expect a 
correlation between all members of a litter at a first level and between all 
individuals sharing a mother at a second superior level with an exchangeable 
matrix. I order my dataframe by both mother and litter

I try several syntaxes:
id= mother*litter which give the same correlation matrix as id= litter*mother
and id=litter with a matrix size of 7*7 which correspond to the maximum number of 
young per litter

id=litter|mother which give the same correlation matrix as id=mother|litter with 
a correlation matrix size of 235*235 which correspond to the number of 
observations

id=litter/mother and id=mother/litter give different result with a strange matrix 
of 11*11 with no 1 on the diagonal

If anybody know if it is possible to construct nesting levels in R and what is 
the good syntax for this kind of model?

Thanks in advance


Aurélie Cohas