Oh, I meant the opposite, that if being schizophrenia-prone made you cannabis-prone (self-medication, effectively), that more people overall smoking pot might not mean that more schizophrenia-prone people were smoking pot, because that population would already be saturated.

I'm not saying that my hypotheses are correct, I'm just pointing out that if we're going to be scientific about whether cannabis induces schizophrenia we need to avoid jumping to conclusions.