According to the latest Partnership Attitude Tracking Survey, the percentage of high school students who said they had ever tried marijuana fell between 2010 and 2011, the percentage reporting past-year use remained the same, and the percentage reporting past-month use rose slightly. But that is not what the press release from the Partnership at Drugfree.org (formerly the Partnership for a Drug-Free America) said. The organization, which sponsors the survey together with the MetLife Foundation, led with this instead: "National Study: Teen 'Heavy' Marijuana Use Up 80 Percent Since 2008, One in Ten Teens Reports Using Marijuana at Least 20 Times a Month."

Sexier, right? News outlets sure thought so:

And so on. Those summaries definitely sound more alarming than, say, "Marijuana Use Among Teenagers Remains Essentially Unchanged." But they're not quite as—what's the word?—true. The increase hyped by the Partnership happened almost entirely between 2008 and 2009. Since then the numbers have been basically flat. Furthermore, the numbers recorded last year are virtually indistinguishable from the numbers recorded in 1998, the earliest year for which the new report includes data.

Data from the Monitoring the Future Study, which is conducted by University of Michigan researchers under contract with the National Institute on Drug Abuse, show a similar pattern: Marijuana use rates are essentially the same now as they were in the late 1990s. In between, they went down and up for reasons that remain unclear but that probably have little to do with anti-drug ads, medical marijuana laws, the number of pot busts, or the federal government's drug control "strategy."

One notable difference between the Partnership Attitude Tracking Survey (PATS) and the Monitoring the Future (MTF) Study: The PATS numbers tend to be higher, especially for "heavy" marijuana use—meaning use on 20 or more days in the previous month, which MTF calls "daily" use. While PATS put "heavy" use at 9 percent of all high school students last year, MTF put it at less than 7 percent for seniors, who are more likely to smoke pot than younger students are. Averaging seniors with 10th-graders, the MTF number is about 5 percent, meaning the PATS number is nearly twice as high. Since the sampled populations are supposed to be about the same, maybe PATS is eliciting more candor—or more exaggeration.

Speaking of which, "daily" marijuana use by high school seniors in the MTF survey peaked at nearly 11 percent in 1978. As I noted in a 1993 Reason article about marijuana reform, such figures should be taken with a grain of salt:

These numbers overstate the percentage of seniors who got stoned every day in the late '70s. First of all, they don't represent actual daily use throughout the year–only use on 20 or more of the previous 30 days. Granted, that's still pretty heavy. But the numbers include kids who had recently gone through a brief period of heavy use. And as Mark Kleiman, associate professor of public policy at Harvard's John F. Kennedy School of Government, notes in Marijuana: Costs of Abuse, Costs of Control, the data are probably inflated by error or exaggeration: Experience with marketing surveys indicates that questions about habitual activities like "On how many of the last 30 days did you use marijuana?" tend to elicit systematic overreporting. Furthermore, the 11-percent "daily use" figure appears to be inconsistent with information from NlDA's household survey.

In any event, the corresponding PATS number, contrary to the impression given by the Partnership's press release and the stories it generated, did not go up in the most recent survey.