>We selected participants eligible for mortality follow-up, aged 20 years and above, who answered “yes” or “no” to the question, “Have you ever used marijuana or hashish?” Participants who answered yes were classified marijuana users and those who answered no, as non-marijuana users. Duration of marijuana use was estimated by subtracting participant’s age at marijuana use initiation from the age at the 2005 screen.

So even if I smoked a single joint since I started smoking, I am put in the the same bucket as someone who smokes weed daily? That doesn't sound right. Am I missing something?