"More schools and students are captured in the HYS [Washington Healthy Youth Survey] than MTF [Monitoring The Future Survey] (Table). The MTF included fewer low–socioeconomic status and nonwhite youth in the prelegalization vs postlegalization period.

"Estimates from the MTF show statistically nonsignificant change in the prevalence of cannabis use for 8th graders (from 6.2% [95% CI, 4.4%-8.7%] to 8.2% [95% CI, 6.3%-10.7%];P = .16), and a significant increase for 10th graders (from 16.2% [95% CI, 14.0%-18.6%] to 20.3% [95% CI, 16.9%-24.1%]; P = .02). In contrast, the HYS shows statistically significant declines in prevalence from 2010-2012 to 2014-2016 among both 8th graders (from 9.8% [95% CI, 9.1%-10.5%] to 7.3% [95% CI, 6.6%-8.0%]; P < .001) and 10th graders (from 19.8% [95%CI, 18.6%-21.0%] to 17.8% [95%CI, 16.7%-18.9%]; P = .01). Neither MTF nor HYS analysis showed changes among 12th graders (Figure). Findings from HYS comparisons to 2014 alone were of less magnitude but similar direction."


Dilley JA, Richardson SM, Kilmer B, Pacula RL, Segawa MB, Cerdá M. Prevalence of Cannabis Use in Youths After Legalization in Washington State. JAMA Pediatr. 2019;173(2):192–193. doi:10.1001/jamapediatrics.2018.4458