[Ken H]

Denver Post, Dec 16, 2014 =>

Teen use of marijuana has not increased in the past four years nationwide, even as the country has undergone a transformation in marijuana's legality and availability, according to the results of a survey released Tuesday.

Instead, the annual Monitoring the Future survey found that various measures of teen marijuana use across the country decreased slightly in 2014.

http://www.denverpost.com/news/ci_27147495/no-increase-teen-marijuana-use-2014-national-survey

[DiogenesLamp]

I put very little credibility in self reporting surveys. Their methodology is to ask high school teens if they have been smoking pot.

There is no obligation from them to tell the truth one way or the other.