I totally agree with your points as to limitations. However, there have been studies that have been able to get up to 21000 individuals with consistency in the concentration of the weed they take. I just can't lay my hands on the link
Although, in places where weed is having legal issues it might not be possible to make correlates however, there are still some significant findings despite the inconsistency and limitations in the topic discussed.
In places like Jamaica, the studies are actually reliable.
I really appreciate your comment and I want to say a big thank you for reading the post.