Sure, but it's entirely possible the schizophrenia-prone population did not alter their pot usage. Also, if there's a link to the amount consumed, the number of individuals smoking pot at all could have increased while the number of individuals smoking enough pot to trigger psychosis and schizophrenia stayed constant. Wider consumption of alcohol doesn't necessarily correlate with more alcoholism.
Yeah, but this population prone to schizophrenia would have: a) to know they're predisposed to this condition; b) to know that weed would worsen it; c) to believe that this effect on schizophrenia would be bad enough to outweigh smoking a joint. Or have another factor linked to schizophrenia that makes them avoid weed. It's possible, in principle, but I think you're stretching it too far.
And it's assumed the distribution of smoking per capita didn't change by much. I think that's a good assumption; again, it's possible that what you suggested happened, but it's a bit sketchy.
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.
