An indirect causal relationship is said to exist if one condition has an effect upon an intermediary factor that, in turn, increases the likelihood of developing the second condition [41]. For example, research has shown that the presence of early onset AOD use reduces the likelihood of completing high school, entering tertiary education, and completing tertiary education [42, 43]. This poor level of education may lead to later life difficulties (e.g., unemployment) that may lead to other problems, such as depression [44, 45]. Similarly, the reverse is possible, whereby a depressive disorder may lead to difficulties completing study and work commitments, which may in turn lead to difficulties finding employment, increasing the risk of problematic levels of AOD use [46–48].