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

[Arne.Muller@aventis.com]

Hello,

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

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