Interesting. My dad developed schizophrenia in his twenties and had been smoking a lot of marijuana. I have always wondered if the smoking triggers something in him. I will always wonder.
The explanation "increased THC content causes more schizophrenia" is clearly more plausible than "more schizophrenia causes increased THC content".
My understanding is that the ratio of THC to CBD is significant; CBD seems to protect against some of the more alarming effects of THC.
In 2000 Denmark was spending 2496$ yearly per capita on healthcare, in 2012 it was 6004$(taking inflation into account: 2496$ in 2000 was 3,327.91$ in 2012)
Maybe they just got better at detecting it?
Your reasoning is akin to saying that it's likely that vaccines cause autism because of some overlapping charts, correlation is not causation.