It looks like this story would be a great case for a critical thinking class.

From the story:

Occasional smokers were 40 per cent more likely to suffer from psychosis, while dedicated tokers who used marijuana daily or weekly increased their risk by 50 to 200 per cent.

From STATS.org:

To epidemiologists a 40% increase is not especially noteworthy– they usually don’t find risk factors worth worrying about until the number hits at least 200% and some major journals won’t publish studies unless the risk is 300 or even 400%.