I am conducting two-way ANOVAs to determine if plant height (mm) is affected by treatment (3 water regimes) in different growth medium types (2). I am also interested in the interactions that may occur between the water treatments and soil so my model is contracted as such.
I have multiple species of plant included in this study. As such, I have decided that the best course of action to statistically analyse the data is to do seperate two-way ANOVAs per species (I am not all that interested in the fact that some plants will be taller than others; its a given). However, after partitioning the data per species, it has become evident that ONLY SOME of the species' heigh values are normal (shapiro.test).
Can I transform the data of ONLY the species that aren't normal? Or should all (even the already normal ones) be transformed?