The mediational model predicts that the causal processes captured by the ‘genes’ to ‘EP’ path are shared between EP and PD. The liability-index model does not make this assumption. Most importantly, the mediational model predicts that if it were possible to change EP with an exogenous variable (for example, a cognitive or pharmacological treatment), doing so would result in a decline in risk for PD. The risk-indicator model makes no such prediction.
