The 2012 University of Michigan study, Monitoring for the Future, reported that 36.4% of current high school seniors had either smoked Marijuana or Hashish.
Back in the 1970's, during my first year of college, I shared a dormitory suite with nine other guys.
Of the ten of us in the dormitory suite, 90% smoked marijuana.
I was the other 10%.
Maybe the incidence of marijuana has actually decreased since the 1970's?
I'll have to check some references.