Dear R - Users
  I have some problems fitting a linear mixed effects model using the lme function (nlme library). A sample data is as shown at the bottom of this mail. I fit my linear mixed model
using the following R code:
   
  bmr <-lme (outcome~ -1 + as.factor(endpoint)+ as.factor(endpoint):trt, data=datt,
      random=~-1 + as.factor(endpoint) + as.factor(endpoint):trt|as.factor(Trial),
     correlation = corSymm(form=~subject|as.factor(endpoint)),  
        weights=varIdent (form=~subject|endpoint))
   
  With this code, i want to obtain random effects for each Trial. ALso my residuals are correlated, and the correlated residuals are  heteroscedastic over endpoint. That is, each endpoint has a different constant variance. 
   
  However, I recieve the following error message using the code above:
   
  Error in lme.formula(outcome ~ -1 + as.factor(endpoint) + as.factor(endpoint):trt,  : 
        Incompatible formulas for groups in "random" and "correlation"
   
  May someone kindly inform me of how to correct my code.
   
  Does this imply that the grouping factor in the correlation formula must be the same grouping factor in the random formula ? If so, is there a way of getting pass this restriction ?
   
  In essence, I wish to know how to fit a linear mixed model with correlated residuals (based on a variable in my model) and to obtain the correlation matrix.
  
Best regards
Pryseley
   
  Sample data:
   
  RowNames Trial subject VISUAL0  TRT VISUAL24 VISUAL52 TREAT outcome endpoint trt 
4      1    1003      65   4       65       55     2       0        1   1 
8      1    1007      67   1       64       68     2      -3        1  -1  
12      2    1110      59   4       53       42     2      -6        1   1  
14      2    1111      64   1       72       65     2       8        1  -1  
16      2    1112      39   1       37       37     2      -2        1  -1   
18      2    1115      59   4       54       58     2      -5        1   1   
24      3    1806      46   4       27       24     2     -19        1   1   
26      3    1813      31   4       33       48     2       2        1   1   
28      3    1815      64   1       67       64     2       3        1  -1   

  4      1    1003      65   4       65       55     2     -10       -1   1     
8      1    1007      67   1       64       68     2       1       -1  -1     
12      2    1110      59   4       53       42     2     -17       -1   1    
14      2    1111      64   1       72       65     2       1       -1  -1    
16      2    1112      39   1       37       37     2      -2       -1  -1   
18      2    1115      59   4       54       58     2      -1       -1   1   
24      3    1806      46   4       27       24     2     -22       -1   1    
26     3    1813      31   4       33       48     2      17       -1   1    
28      3    1815      64   1       67       64     2       0       -1  -1     
   
   
  Thanks 
   
   
   
   
  
 

		
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