不平衡数据集上的双向anova

Question

Is aov appropriate for 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.

Answer 1

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 .