It is especially difficult to determine the nature of the link between drugs and crime, and particularly whether one behaviour is sufficient for the other to occur (a strict causal relationship) or merely necessary (a weak causal relation).
Is deacra arís nádúr an naisc a chinneadh idir drugaí agus coireanna, agus go háirithe más leor iompar amháin a bheith ann le go dtarlódh an t-iompar eile (gaol atá go hiomlán cúisíoch) nó riachtanach, go díreach (gaol lag cúisíoch).