[R] repeated measures aov problem

[Nathan Weisz]

Hi all,

I have a strange problem and rigth now I can't figure out a 
solution.

Trying to calculate an ANOVA with one between subject factor (group) 
and one within (hemisphere). My dependent variable is source 
localization (data). My N = 25.

My data.frame looks like this:
> ML.dist.stack
   subj group hemisphere      data
1     1   tin       left 0.7460840
2     2   tin       left 1.0300600
3     3   tin       left 0.8026865
<<SNIP>>
47   22   con      rigth 0.6808010
48   23   con      rigth 1.2291490
49   24   con      rigth 2.0930595
50   25   con      rigth 1.5631695

> str(ML.dist.stack)
`data.frame':	50 obs. of  4 variables:
 $ subj      : Factor w/ 25 levels "1","2","3","4",..: 1 2 3 4 5 6 7 
8 9 10 ...
 $ group     : Factor w/ 2 levels "con","tin": 2 2 2 2 2 2 2 2 2 2 
...
 $ hemisphere: Factor w/ 2 levels "left","rigth": 
1 1 1 1 1 1 1 1 1 1 ...
 $ data      : num  0.746 1.030 0.803 2.197    NA ...

Typing: summary(aov(data ~group * hemisphere + Error(subj/
hemisphere), data=ML.dist.stack))
gives me following result ...
Error: subj
                 Df  Sum Sq Mean Sq F value Pr(>F)
group             1  0.1813  0.1813  0.2012 0.6584
hemisphere        1  0.1937  0.1937  0.2149 0.6477
group:hemisphere  1  0.0898  0.0898  0.0996 0.7554
Residuals        21 18.9277  0.9013               

Error: subj:hemisphere
                 Df  Sum Sq Mean Sq F value Pr(>F)
hemisphere        1  1.0534  1.0534  1.6736 0.2105
group:hemisphere  1  0.5714  0.5714  0.9077 0.3521
Residuals        20 12.5893  0.6295               
... which looks like the error strata are wrong.

I kept very close (in my opinion exactly) to Baron's Example 4 of 
the tutorial (p. 29), which produces correct results. See below:
> str(Ela.uni)
`data.frame':	96 obs. of  5 variables:
 $ effect: num  19 11 20 21 18 17 20 14 16 26 ...
 $ subj  : Factor w/ 16 levels "s1","s10","s11",..: 
1 9 10 11 12 13 14 15 16 2 ...
 $ gp    : Factor w/ 2 levels "gp1","gp2": 1 1 1 1 1 1 1 1 2 2 ...
 $ drug  : Factor w/ 2 levels "dr1","dr2": 1 1 1 1 1 1 1 1 1 1 ...
 $ dose  : Factor w/ 3 levels "do1","do2","do3": 1 1 1 1 1 1 1 1 1 1 
...
> summary(aov(effect ~ gp * drug * dose + Error(subj/(dose+drug)), 
data=Ela.uni))

Error: subj
          Df Sum Sq Mean Sq F value  Pr(>F)  
gp         1 270.01  270.01  7.0925 0.01855 *
Residuals 14 532.98   38.07                  
---
Signif. codes:  0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Error: subj:dose
          Df Sum Sq Mean Sq F value    Pr(>F)    
dose       2 758.77  379.39 36.5097 1.580e-08 ***
gp:dose    2  42.27   21.14  2.0339    0.1497    
Residuals 28 290.96   10.39                      
---
Signif. codes:  0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Error: subj:drug
          Df Sum Sq Mean Sq F value   Pr(>F)   
drug       1 348.84  348.84  13.001 0.002866 **
gp:drug    1 326.34  326.34  12.163 0.003624 **
Residuals 14 375.65   26.83                    
---
Signif. codes:  0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Error: Within
             Df  Sum Sq Mean Sq F value Pr(>F)
drug:dose     2  12.063   6.031  0.6815 0.5140
gp:drug:dose  2  14.812   7.406  0.8369 0.4436
Residuals    28 247.792   8.850               

Can someone give me a hint where I migth be going wrong? However 
trivial this migth be I somehow got stuck.

All the best,
Nathan

-----------------------------------------
Nathan Weisz
Department of Psychology
University of Konstanz
P.O. Box D25
D - 78457 Konstanz
GERMANY

Tel: +49 (0)7531 88- 4612
E-mail: Nathan.Weisz at uni-konstanz.de
http://www.clinical-psychology.uni-konstanz.de