[R-sig-eco] Regression with few observations per factor level

[V. Coudrain]

Hi, I would like to test the impact of a treatment of some variable using regression (e.g. lm(var ~ trt + cov)).  However I only have four observations per factor level. Is it still possible to apply a regression with such a small sample size. I think that i should be difficult to correctly estimate variance.Do you think that I rather should compute a non-parametric test such as Kruskal-Wallis? However I need to include covariables in my models and I am not sure if basic non-parametric tests are suitable for this. Thanks for any suggestion.
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