Study on Teen Pot Use Goes Up in Smoke, Then Reappears

A JAMA journal has retracted and replaced a widely circulated 2021 paper which purported to find that pot use among adolescents drops when states make the drug legal.

The article, “Association of Marijuana Legalization With Marijuana Use Among US High School Students, 1993-2019,” appeared in JAMA Network Open and received a bale of attention in mainstream and social media. As GreenEntrepreneur reported:

A September 2021 study of high school use between 1993 and 2019 used the Youth Risk Behavior Survey (YRBS) to determine that adult-use laws did not increase teen use. After two years, states with adult-use laws saw decreases in usage.

But as readers soon pointed out, the findings were schwag. According to the notice:

On behalf of our coauthors, we write to respond to concerns raised about the methods and analyses for the Research Letter, “Association of Marijuana Legalization With Marijuana Use Among US High School Students, 1993-2019,” published in JAMA Network Open on September 7, 2021.
These concerns were brought to our attention by readers and subsequently published as Comments with the article.
In this study, we used data from the Youth Risk Behavior Survey (YRBS) for the period 1993 to 2019 to provide updated estimates of the association of legalization of recreational marijuana and legalization of medical marijuana with adolescent marijuana use.

The statement then goes into detail about the nature of the error, which, once corrected, led the researchers to conclude:

After reconducting the analyses with weighted and unpooled data, RML adoption and MML adoption were no longer statistically significantly associated with adolescent marijuana use. Moreover, in the corrected analysis, we found that 4 or more years after MML adoption, marijuana use among adolescents declined (OR, 0.83; 95% CI, 0.68-0.99; P = .049), as noted in the Figure in the replacement article.

We apologize to the readers and editors of JAMA Network Open for any confusion we caused by conducting our prior analysis based on unweighted and pooled data when the YRBS recommends that the correct approach is to use weighted and unpooled data.

In an email, which we’ve made available in full here, co-authors Joseph Sabia and D. Mark Anderson said economists and clinicians have different views of how to present weighted and unweighted data:

While applied microeconomists are very nuanced and careful in our academic discussions surrounding weighting, our experience is that physicians are more interested in only showing weighted policy estimates, which we were happy to provide in the revised article.

But the bottom line, they said, was that the conclusions of the paper didn’t change after the weighting:

The above quoted conclusion from our original paper reflects the conclusion of our revised paper. We find no evidence from the YRBS data — whether the estimates are weighted or unweighted, are derived from “pooled or separate” national or state YRBS data, or following economists’ conventional empirical practices or physicians’ preferred approaches — that the legalization of marijuana has (as yet) encouraged youth marijuana use.

We learned a great deal from going through this exercise with the editors, in particular how important it is for researchers across disciplines to be able to talk to one another about technical, nuanced applied econometric issues.

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