[R] one-way ANOVA model, with one factor, an unbalanced design and unequal variances

From: Steven <stevenworthington_at_hotmail.com>
Date: Thu, 21 Apr 2011 11:28:06 -0700 (PDT)


Hi,

i'm looking for an R function to fit a one-way ANOVA with one factor containing 10 levels. The factor levels have different numbers of observations (varying between 20 to 40). For most of the dependent variables i'm testing there are unequal variances among the factor levels.

I see the function oneway.test:

oneway.test(variable ~ factor, data=dataset)

which by default does not assume equal variances. I also see the basic ANOVA function (aov), which, I think, is OK for unbalanced designs. I get a different F ratio, however, when using these two functions on the same data, which seems to indicate that the aov function assumes equal variances.

My question: is there an R function that performs a one-way ANOVA while not assuming a balanced design *or* equal variances? Does the oneway.test function, for example, assume a balanced design?

Thanks,

Steven

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