2-way anova on unbalanced dataset
Is aov
appropriate f开发者_开发知识库or unbalanced datasets. According to help ...provides a wrapper to lm for fitting linear models to balanced or unbalanced experimental designs
. But later on it says aov is designed for balanced designs, and the results can be hard to interpret without balance
.
How should I perform a 2-way anova on an unbalanced dataset in R?
I would like to reproduce the different results for type I and type III sum of squares of SAS
output (when using proc glm
). I remember we were using type III sum of squares
for unbalanced datasets.
Thank you in advance.
Function anova
(or summary.aov
) will give you the so called type I (or sequential) sum of squares. To get type III sum of squares, you can use the Anova function from library car
with parameter type="III"
. The difference between these two approaches in unbalanced datasets (and also sample R code to produce both tables) is presented in detail here.
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