[R] unbalanced one-way ANOVA

[Douglas Bates]

On Thu, Feb 28, 2008 at 7:52 AM, Nauta, A.L. <A.L.Nauta at students.uu.nl> wrote:
> Hi,

>  I have an unbalanced dataset on which I would like to perform a one-way anova test using R (aov). According to Wannacott and Wannacott (1990) p. 333, one-way anova with unbalanced data is possible with a few modifications in the anova-calculations. The modified anova calculations should take into account different sample sizes and a modified definition of the average. I was wondering if the aov-function in R is suitable for one-way anova on unbalanced data.

Yes.

The analysis of variance is performed in R by fitting a linear model
created from indicator variables for the levels of the factor.  This
validity of this approach does not depend on balance in the data.

The formulas given in an introductory textbook are almost never the
way that results are computed in practice.  I think we would all be
better off if they didn't even give these misleading formulas.