We tried to simplify model 19 by reducing either the number of genetic (#20) or unique environmental (#21) common factors, but the AIC deteriorated considerably for both these models. We added to model 19 a third individual-specific environmental common factor (#22) and that also failed to improve the fit. Finally, we also added to model 19 a fourth genetic factor (#23). This also did not improve the AIC. Model 19 was clearly our best-fit model.
