The drop from ever used, to used in last month, to chronic use is very large and consistent with the observation that occasional use dies out.
To my mind, use once in the last year is essentially no use.
Occasional use is much more frequent than once in a year to my mind.
There is also a problem in these studies. People who may use dope once a year very well do not feel effects, because they are doing it socially, don’t inhale much or take many tokes etc...
These studies should really be focused on getting stoned, the full effect.
Data on that may be