Despite a claim made by a panelist at a discussion on retail marijuana hosted by the League of Women Voters on June 1, experts are divided on the relationship between marijuana dispensary density and teen use.

The original assertion made by Dr. Eden Evins, director of the Center for Addiction Medicine at Massachusetts General Hospital, was part of her response to a question about when the density of marijuana dispensaries started to impact teen use.

“It’s a linear correlation, so there’s not, like, a certain ceiling, you know, a sort of break point where it doesn’t make a difference,” Evins said.

When the Concord Journal asked for the study that showed this relationship, Evins directed us to a slideshow created by Smart Approaches to Marijuana, a nonprofit group opposed to legalization.

For data about dispensary density’s affect on teen use, the slideshow referred to an article by Addy Hatch, which cited Julia Dilley, a University of Washington researcher.

“For 11th graders, 16 percent reported recent marijuana use in less-dense areas, while 24.3 percent reported recent use in the areas with the highest retail density,” Hatch wrote.

In an email exchange with Dilley about the Oregon data, she wrote that the relationship described in Hatch’s article were “based on cross-sectional associations between local policy/density and youth use for a single year after markets opened” in Oregon.

Dilley wrote the relationship was best described as an association, but was not a linear correlation and added that “associations are not necessarily causal.”

“So if communities with more relaxed social norms also have more liberal policies, which influence retail density, and separately influence youth use, it would be wrong to say the local policy/retail CAUSED youth use,” Dilley wrote.

Dilley said she is part of a research study on more local impacts of policy

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