That comparison, which comes from a report that the Rocky Mountain High Intensity Drug Trafficking Area (RMHIDTA) issued in January, is popular among opponents of legalization. But it does not tell us nearly as much as Feinstein thinks.
RMHIDTA, an anti-drug task force whose annual reports on legalization in Colorado are
designed to show what a disastrous mistake it was, provided the numbers cited by Feinstein in an
update to its
2015 report. They come from the National Survey on Drug Use and Health (NSDUH), which samples Americans 12 and older. When you focus on teenagers and break the numbers down by state, the samples are quite small, which is why NSDUH pools data for two years at a time.
For 2011-12, the two years before legalization, the rate of past-month marijuana use (a.k.a. “current” use) among 12-to-17-year-olds in Colorado was 10.5%. That number rose to 12.6% in 2013-14, the first two years in which marijuana was legal for recreational use. “In the two year average (2013/2014) since Colorado legalized recreational marijuana,” RMHIDTA says, “youth past month marijuana use increased 20 percent compared to the two year average prior to legalization (2011/2012).”
As it tends to do, RMHIDTA leaves out an important piece of information that weakens its case against legalization: The increase it highlights was not statistically significant. If you look at
this NSDUH report from December, you can see that the pre-legalization estimate (10.5%) falls within the 95% confidence interval for the post-legalization estimate (10.3% to 15.2%). In other words, given the potential for sampling error, we cannot say with 95% confidence (the usual standard) that the increase Feinstein deems “very big” actually happened. The confidence intervals for the state-specific NSDUH numbers are pretty wide, reflecting the small sample sizes, which makes it hard to distinguish real trends from sampling variation.
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