As a population based study, how did they control for other substances? Acid in particular is notorious for flashbacks years later that can be psychotic. I also note that the period in question is also associated with massive increase in methamphetamine abuse. Greater access to THC being associated with an increase in crazy people using it makes complete sense, but is a causal link between legislation and schizophrenia really demonstrated amongst chronic potheads (the study is about psychosis in people with CAD), that being the subject of the paper?