In Model 3 (Figure 3) none of the association between availability, initiation and abuse is due to correlated latent, genetic and environment effects. Instead, the association occurs entirely at the phenotypic level either directly via β3, or indirectly via β1 through initiation and along the β2 pathway. β3 represents any direct influence of availability on abuse that does not influence initiation. Model 4 predicts that β3 is non-significant i.e., β3 = 0.
