[R] Problem in lme4

[Douglas Bates]

Doran, Harold wrote:


> I was able to run the following in nlme successfully, but the same model
> and code (same dataset) failed to run in lme4 and gave me the error
> message below. Any thoughts?
>  
> 
> lme(math~year, data=egsingle, random=~year|schoolid/childid)
>  
> 
> Error in lme(formula = math ~ year, data = egsingle, random =
> structure(list( : 
> 
>         Unable to invert singular factor of downdated X'X

Is childid unique?  If not, you will need to generate a unique id for 
the child for the lme4 version of lme.  (This change is required because 
the lme4 package can fit models with crossed or partially crossed 
grouping factors.)

A simple way of creating the necessary factor (thanks to Martin Maechler 
for showing me this) is

egsingle$chld <- (egsingle$schoolid : egsingle$childid)[drop = TRUE]

(I haven't checked this.  I don't have R on the machine that I use for 
email connectivity.  I can check this later today.  Is the egsingle data 
set the same one you sent me earlier?)