R help - Jan 2009 - getResponse(model.lme) yields incorrect number of dimensions error

Dear R experts,

I would like to get an R^2 - like value for a multilevel regression using lme.

I followed an archived suggestion by José 
Pinheiro to use the squared correlation between 
fitted and observed values, i.e.,

(cor(fitted(model.lme), getResponse(model.lme))^2

but getResponse returns the error message

Error in val[, level] : incorrect number of dimensions


The same happens with residuals(model.lme) and 
summary(model.lme) but not other generic 
functions such as predict, coef, or fitted, which (seem to) work fine.

I have searched the archives but could not find a 
solution--I don't really understand what dimensions R is referring to.

Any comments or suggestions would be greatly appreciated!

Thanks for your time, and happy new year,

Ullrich



Below is part of the dataframe and the code:


 > WMUCTrim
     Subj Cond       Acc S R T
1      1    1 0.6666667 1 1 1
2      1    2 0.8095238 1 0 1
4      1    4 1.0000000 1 0 0
6      1    6 0.9523810 0 0 1
7      1    7 0.8571429 0 1 0
8      1    8 1.0000000 0 0 0
209    2    1 0.3809524 1 1 1
210    2    2 0.9047619 1 0 1
212    2    4 1.0000000 1 0 0
214    2    6 0.8571429 0 0 1
215    2    7 0.6666667 0 1 0
216    2    8 1.0000000 0 0 0

 > mlr2 <- summary(lme(Acc ~ R + T + S, random = ~1 | Subj))
 > mlr2
Linear mixed-effects model fit by REML
  Data: NULL
         AIC       BIC   logLik
   -1140.414 -1113.778 576.2068

Random effects:
  Formula: ~1 | Subj
         (Intercept)   Residual
StdDev:  0.07069723 0.08233792

Fixed effects: Acc ~ R + T + S
                  Value   Std.Error  DF   t-value p-value
(Intercept)  0.9843537 0.008937809 522 110.13367  0.0000
R1          -0.1139456 0.006958824 522 -16.37426  0.0000
T1          -0.1012472 0.006958824 522 -14.54946  0.0000
S1          -0.0137188 0.006958824 522  -1.97143  0.0492
  Correlation:
    (Intr) R1     T1
R1 -0.260
T1 -0.260  0.000
S1 -0.260  0.000 -0.333

Standardized Within-Group Residuals:
         Min          Q1         Med          Q3         Max
-4.21190127 -0.46318153  0.02715579  0.58591808  2.57708969

Number of Observations: 630
Number of Groups: 105
 > class(mlr2)
[1] "summary.lme" "lme"
 > cor(fitted(mlr2), getResponse(mlr2))^2
Error in val[, level] : incorrect number of dimensions



Dr Ullrich Ecker | Postdoctoral Research Fellow | 
Cognitive Science Laboratories | Room 211 Sanders Building |

* School of Psychology | M304 | The University of 
Western Australia | 35 Stirling Highway | Crawley WA 6009 | Australia |
( 08 6488 3266 | Ê 08 6488 1006 | À 04 5822 0072 
| @ ullrich.ecker@uwa.edu.au | i www.cogsciwa.com |  
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