So smoking skunk cause psychosis, but milder cannabis doesn't?

Research that looks at different potencies of cannabis could advance our understanding of the relationship between the drug and psychosis
The Guardian (UK)
Monday, February 16, 2015

The Mail on Sunday has shouted that "cannabis TRIPLES psychosis risk" and that skunk is to blame for "1 in 4 of all new serious mental disorders". Is this what the study shows? Well, no, they found that those with psychosis were much more likely to have used skunk every day, than to have never used cannabis. Conversely, people who smoked hash every day were no more likely to have psychosis than people who never tried cannabis. (See also: What media reports on the new cannabis study don't tell you | Why cannabis studies are needed | Skunk's psychosis link is only half the cannabis story)