[R] singular convergence with lmer function i lme4

[Arild Husby]

Dear R users,


I am trying to fit a GLMM to the following dataset;


tab
   a   b            c
1  1 0.6 199320100313
2  1 0.8 199427100412
3  1 0.8 199427202112
4  1 0.2 199428100611
5  1 1.0 199428101011
6  1 0.8 199428101111
7  0 0.8 199527103011
8  1 0.6 199527200711
9  0 0.8 199527202411
10 0 0.6 199529100412
11 1 0.2 199626201111
12 2 0.8 199627200612
13 1 0.4 199628100111
14 1 0.8 199628101511
15 1 0.4 199726200212
16 1 0.2 199726202111
17 1 0.6 199727101411
18 2 0.6 199727106911
19 2 0.6 199728100212
20 0 0.4 199820100811
21 1 0.8 199826200611
22 2 0.6 199827203811
23 2 1.0 200038109911
24 0 0.6 200126202511
25 0 0.4 200226100311
26 1 0.6 200226100411
27 1 0.4 200226100611
28 1 0.4 200226126011
29 1 0.4 200226203712
30 2 0.6 200227220313


With the following model;

  lmer(a~b + (1|c), family=poisson, data=tab),

What I want to do is to see if number of recruits (a) is dependent on the
brood sex ratio (b) including brood identity (c) as random factor.


However, I get the following error message;

lmer(a~b + (1|c), family=poisson, data=tab)
Error in devAGQ(PQLpars, 1) : Unable to invert singular factor of downdated
X'X
In addition: Warning messages:
1: optim or nlminb returned message singular convergence (7) 
 in: LMEopt(x = mer, value = cv) 
2: optim or nlminb returned message singular convergence (7) 
 in: LMEopt(x = mer, value = cv) 
3: optim or nlminb returned message singular convergence (7) 
 in: LMEopt(x = mer, value = cv) 
4: optim or nlminb returned message singular convergence (7) 
 in: LMEopt(x = mer, value = cv) 
5: optim or nlminb returned message singular convergence (7) 
 in: LMEopt(x = mer, value = cv) 
6: optim or nlminb returned message singular convergence (7) 
 in: LMEopt(x = mer, value = cv) 
7: IRLS iterations for PQL did not converge


I do not understand what causes this error message, all help is highly
appreciated!



I am running R version 2.20 on win XPP.
> version
         _              
platform i386-pc-mingw32
arch     i386           
os       mingw32        
system   i386, mingw32  
status                  
major    2              
minor    2.0            
year     2005           
month    10             
day      06             
svn rev  35749          
language R  


lme4 package version: 0.98-1
Matrix version: 0.98-7
lattice version: 0.12-11



Best regards,

Arild