[R] unbalanced design for anova with low number of replicates

Arne.Muller@aventis.com Arne.Muller at aventis.com
Mon Jun 28 11:45:49 CEST 2004


I'm wondering what's the best way to analyse an unbalanced design with a low number of replicates. I'm not a statistician, and I'm looking for some direction for this problem.

I've a 2 factor design:

Factor batch with 3 levels, and factor dose within each batch with 5 levels. Dose level 1 in batch one is replicated 4 times, level 3 is replicated only 2 times. all other levels are replicated 3 times, except for batch level 3, for which dose 4 is missing. 

I've realised that the other of the factors is critical for the outcome of the anova (using lm and anova).

I guess the impact wouldn't be strong if there was a reasonably large numbe rof replicates within each cell (even though not balanced). However, since I've only 0 to 4 replicates I'm worried that the standard anova may not be the way to go.

Are there special packages for unbalanced designs like this?

	kind regards,


Arne Muller, Ph.D.
Toxicogenomics, Aventis Pharma
arne dot muller domain=aventis com

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