I want to know if this is a reasonable approach. I conducted the same experiment on two different species with small sample sizes (7-25 per species) in 4 years at 6 different sites. I measured damage to plants in two treatments.
There is unequal sampling across years and sites. Species, site and year differ in mean damage levels. The data are highly non-normal.
what I did:
- I got the residuals of a model damage= species +site(species) as a random effect + year
- Then I used a Wilcoxon rank sum test to test differences between treatments.
Does this seem reasonable?