[R] problem with geepack

[Giacomo Santini]

Hi all

I am analyzing a data set containing information about the behaviour of 
marine molluscs on a vertical wall. Since I have replicate observations 
on the same individuals I was thinking to use the geepack library.

The data are organised in a dataframe with the following variables

Date = date of sampling,
Size = dimensions (mm)
Activity duration of activity (min)
Water = duration of splashing by waves
Hgt = resting eight of each specimen before activity begin
Individual = a code indicating the id of the specimen.

I have up to 12 replicate observations for individual. Some observation 
are missing and I organized the data frame to have exactly 12 rows for 
each specimen, with NAs where there is a missing observation.

The following model worked fine:

gee1<-geese(Activity~Water, id=Individual, data=dataF, family=gaussian)

but when I use other variables e.g

gee2<-geese(Activity~Hgt+Size+Water, id=Individual, data=dataF, 
family=gaussian)

I get the error message

"Error in geese.fit(x, y, id, offset, soffset, w, waves, zsca, zcor, 
corp,  :
  nrow(zsca) and length(y) not match"

which I am not able to understand.

The same problem has been reported in the list in 2006, but I have not 
found any response to it.

Any suggestion?


Giacomo