The association between cannabis and schizophrenia remains, as far as I'm aware, primarily statistical, and other factors like familial history are significantly more predictive.

EDIT: That is, I don't think we have sufficient understanding to say whether pot abuse causes schizophrenia, or schizophrenics are more likely to abuse pot. Given what I know of how awful a ride that is, self-medicating that devolves into abuse seems far more plausible to me. Further, there's research that takes into account family history of these mental illnesses out to 3rd — and further — degrees, and which suggests a much stronger link between that and the illness, than the drug use.