Hi,
Dealing with a repeated measure ANOVA with NAs, I am a bit surprised by S+
output (S+6 as well as S+2000 on Win98). Example:
## anova with repeated measure. Works fine
> summary (aov(formula = mctend ~ Time + Error(Sujet/Time), data = c3))
Error: Sujet
Df Sum of Sq Mean Sq F Value Pr(F)
Residuals 39 37.72124 0.9672114
Error: Time %in% Sujet
Df Sum of Sq Mean Sq F Value Pr(F)
Time 2 0.81571 0.407857 0.3797048 0.6853207
Residuals 78 83.78317 1.074143
## Adding an NA
> c3$mctend[45] <- NA
## without specification for the treatment of the NA, the procedure stop. Fine
> summary (aov(formula = mctend ~ Time + Error(Sujet/Time), data = c3))
Error in function(object, ...): missing values not allowed: found in mctend
## But when we exclude the NA, the error is divided in 3 parts (including an
na.action!), and the factor Time is tested twice !!
> summary (aov(formula = mctend ~ Time + Error(Sujet/Time), data = c3,
> na.action=na.exclude))
Error: Sujet
Df Sum of Sq Mean Sq F Value Pr(F)
Time 1 0.59182 0.5918184 0.6126098 0.4386575
Residuals 38 36.71031 0.9660609
Error: Time %in% Sujet
Df Sum of Sq Mean Sq F Value Pr(F)
Time 2 0.80665 0.403327 0.3706737 0.6914941
Residuals 77 83.78298 1.088091
Error: na.action
Min. 1st Qu. Median Mean 3rd Qu. Max.
45 45 45 45 45 45
Is this a bug or my misunderstanding of repeated measure? In the first case, is
it possible to compute separately the covariance matrix with an EM-algorithm
for the missing values and to feed aov with it? Any other solution is also
welcomed.
Olivier
--
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Olivier Renaud mailto:Olivier.Renaud@pse.unige.ch
Faculty of Psychology and Education Tel: +41 22 705 9104
University of Geneva - 40, Bd du Pont d'Arve - CH-1211 Geneva 4
http://www.unige.ch/fapse/PSY/persons/prof-ana/
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