To model the effects of continuous moderators in Mx, Purcell (http://statgen.iop.kcl.ac.uk/gxe/) has made available a series of moderation models, which are based on previous models by Martin et al.(Martin et al., 1987; Purcell, 2002). In these models, the total variance V= [A+X*M]2 + [C+Y*M]2 + [E+Z*M]2 where A, C, E, X, Y and Z are freely estimated and X, Y and Z denote the moderation effects.
