If cannabis is getting stronger, why aren't cases of schizophrenia rising?

Smoking cannabis has been linked with schizophrenia – and 94% seized in Britain in 2016 was of the high-potency variety.
Read more: https://theconversation.com/if-cannabis-is-getting-stronger-why-arent-cases-of-schizophrenia-rising-93032?source=Snapzu