A study published in September in JAMA Network Open, a peer-reviewed publication under the American Medical Association umbrella, found “little evidence” that adult and medical use cannabis legalization “encourage youth marijuana use.”
It was a compelling study, and Cannabis Wire interviewed the lead author by email for our coverage. On Tuesday, the journal published a “Notice of Retraction and Replacement.” Methodological concerns raised by researchers prompted a new data analysis, which made the declines in youth use no longer “statistically significant.”
“We apologize to the readers and editors of JAMA Network Open for any confusion we caused,” the authors wrote in the notice.
So what happened? Importantly, the authors of the original study used “unweighted and pooled national and state” data from the Youth Risk Behavior Survey for the time frame 1993 to 2019, a time period when states overhauled their cannabis laws, starting with California in 1996.
It was this “pooling” of data that was the problem.
“While this unweighted and pooled approach maximized the number of state policy changes used to identify the effect of marijuana legalization on youth marijuana use for the average student in the pooled sample, published Comments advised that the approach was inappropriate,” authors Mark Anderson and Joseph Sabia wrote in a letter published Tuesday.
One of the researchers who wrote a comment of concern was Nora Volkow, director of the National Institute on Drug Abuse.
“The ability to review, respond to, and when needed, retract published journal articles is an important part of the research process, and helps to maintain the integrity and trustworthiness of scientific literature,” Volkow told Cannabis Wire. “As noted in the original comment, my colleagues and I had several concerns about the validity of the study and its findings, which we felt warranted a formal response. It is crucial that we have reliable data if we are to understand the impact of legalization on substance use among young people.”
The authors of the youth use study noted that commenters expressed concern by writing that “pooling national and state YRBS data is inappropriate because underlying person-level weights are different, and there is some overlap between national and state YRBS data; thus, a student could be represented more than once. The YRBS codebook explicitly warns against combining these data.”
The editors of the publication requested that the study authors conduct a new analysis that used weighted and unpooled data, which produced different results.
“We had previously reported that medical marijuana law (MML) adoption was associated with a statistically significant decrease in the odds of marijuana use among adolescents and that 2 or more years after adoption, recreational marijuana laws (RMLs) were associated with a statistically significant decrease in the odds of marijuana use among adolescents,” the authors wrote. When the researchers did the analyses again, adoption of adult and medical use laws “were no longer statistically significantly associated with adolescent marijuana use.”
The updated research concluded by noting that adult use laws are a “relatively new phenomenon, and as more recent post legalization data become available, further research will be needed to better define the associations between RMLs and adolescent marijuana use.”