"Nowhere do they say anything close to '85% of Americans use marijuana'."
I said 'have used' in my original comment, which is what I meant. (In my reply I was thinking lifetime prevalence, i.e. around 85% 'use' marijuana at some point during their lives. Poorly phrased, my bad.)
"Among current 18-year-olds, only 42% have ever tried marijuana even once."
The age of first use of marijuana is highly variable. By age 25 around 65% of people have used marijuana, and more people keep trying throughout the next couple decades of their life. The important statistic is what percentage of people use marijuana at least once in their lives, not what percentage use it on any given day.
"On page 103, it says that 82% of fifty-year-olds (who attended high school during the heaviest-drug-using period in America's recent history) have used marijuana at least once in their lives."
The 82% figure doesn't count people who didn't make it to fall of their 12th grade year in high school, so you actually have to adjust it up a couple percentage points. Also, even if less high schoolers were using illegal drugs for a decade or two, that probably won't have much effect on the overall lifetime prevalence. It might eventually decline a few points, but probably not that much.
I said 'have used' in my original comment, which is what I meant. (In my reply I was thinking lifetime prevalence, i.e. around 85% 'use' marijuana at some point during their lives. Poorly phrased, my bad.)
"Among current 18-year-olds, only 42% have ever tried marijuana even once."
The age of first use of marijuana is highly variable. By age 25 around 65% of people have used marijuana, and more people keep trying throughout the next couple decades of their life. The important statistic is what percentage of people use marijuana at least once in their lives, not what percentage use it on any given day.
"On page 103, it says that 82% of fifty-year-olds (who attended high school during the heaviest-drug-using period in America's recent history) have used marijuana at least once in their lives."
The 82% figure doesn't count people who didn't make it to fall of their 12th grade year in high school, so you actually have to adjust it up a couple percentage points. Also, even if less high schoolers were using illegal drugs for a decade or two, that probably won't have much effect on the overall lifetime prevalence. It might eventually decline a few points, but probably not that much.