[R] random slope models with lme --> failured to converge

[anord]

Dear all, 

I am working on a data set in which I have sequentially measured egg
temperatures ("eggtemp") in birds incubating in different ambient
temperatures ("treat", sample data set below), "id" is not replicated within
treatment. 

    id treat  eggtemp
1   79     3 30.90166
2   42     3 34.94044
3   10     3 32.69945
4  206     3 36.64127
5   23     3 31.80055
6    5     3 29.98338
7   24     3 35.72992
8   45     3 30.49584
9   29     3 33.64958
10  78     3 31.37673
11  44     3 32.85873
12 368     3 34.44875
13  79     4 31.24100
14  42     4 34.11634
15  10     4 34.73407
16 206     4 36.20914
17  23     4 34.98061
18   5     4 34.17590
19  24     4 37.71468
20  45     4 35.34765
21  29     4 35.48892
22  78     4 33.26593
23  44     4 34.86981
24 368     4 34.44875
25  79     2 27.33241
26  42     2 30.73269
27  10     2 29.54986
28 206     2 31.78947
29  23     2 29.69114
30  24     2 36.48199
31  45     2 29.76454
32  29     2 30.56510
33  78     2 27.71468

For this data, I want to construct a model with a random intercept and slope
to compare with a model containing only the random intercept to check
whether or not different individuals respond differently to treatment.
> temp2.lme<-lme(eggtemp~treat,random=~treat|id,data=temp3.df)

However, I get the below error, which I suspect might be because individuals
are not replicated within treatments.
 > nlminb problem, convergence error code = 1
   message = iteration limit reached without convergence (9)

If I specify treatment as a factor (which it really is not, just different
ambient temperatures), the model seems to converge. Similarly, the model
converges if I exclude one of the treatment levels. However, this does not
feel very satisfactorily. 

So, how do I move on from here? Any tips and hints are much appreciated. I
have tried to include the random slope only, which also works, but the
inference for such a model would be quite different and not really what I am
after.
> temp3.lme<-lme(eggtemp~treat,random=~treat-1|id,data=temp3.df)

Kind regards, 
Andreas Nord
Lund University
Sweden

-- 
View this message in context: http://n4.nabble.com/random-slope-models-with-lme-failured-to-converge-tp1469575p1469575.html
Sent from the R help mailing list archive at Nabble.com.