Actually, the press has been confusing correlation with causation
(again) when it comes to the issue of schizophrenia and marijuana use.
The fact remains that those who are going to develop one of the forms
(there are many, another thing the press misses, among so many details)
of schizophrenia may be feeling pretty rotten for a number of years
beforehand, and will seek out intoxicants to help ease their discomfort.
Now the press loves to beat up a story where one doesn't exist,
particularly if they can conveniently omit the facts that make the story
so much less interesting such as in this case. Despite people waving
papers around saying that there is an arrow of causation in this
correlation, there just isn't, and it's unlikely to ever be
satisfactorily answered because we can't (ethically) take a lot of
twelve year olds, test to predict who will develop schizophrenia, and
then give all of them marijuana and see if it really does accelerate
symptoms in those with a predisposition to develop it. Another group in
this study would be monitored to see if those who were predicted to
develop schizophrenia turned to increased canabis use as their early
symptoms become more prevalent. I don't think watching ill youngsters
abuse drugs without intervention is going to get a whole lot of research
money. Don't believe the hype, the press gets scientific research wrong
all the time: they are usually grossly underqualified/undereducated to
understand what's going on, and they just parrot the researchers at the
press conference (and some researchers just LOVE making pointless press
conferences because they want to be more public to get more grant
money...among other sources of revenue from contentious and popular issues).

Regards,

Ari