Sorry about your roommate but that is anectdata.
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.
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.