I am working on the analysis of biomass growth of plant (dependent variable) for different clones (independent variable) and locations (independent variable). When I do a univariate test it appears that interaction takes places between the two independent variables.
Due to the interaction I make an analysis for the simple main effect.
Now I want to know or the clones differ in biomass within a site. I know that it is possible to do this analysis with splitting the data, but in that case a lot of degrees of freedom get lost. I know that it is possible in SAS when slicing the data, but don´t know how to do this in SPSS.
Is it possible to investigate the difference between clones within a site while using all the data, to keep all the degrees of freedom?
I use SPSS statistics 17.0