NEW YORK (AP)
-- A new analysis is challenging a report that suggests regular
marijuana smoking during the teen years can lead to a long-term drop in
IQ. The analysis says the statistical analysis behind that conclusion is
flawed.
The original study, reported last
August, included more than 1,000 people who'd been born in the town of
Dunedin, New Zealand. Their IQ was tested at ages 13 and 38, and they
were asked about marijuana use periodically between those ages.
Researchers
at Duke University and elsewhere found that participants who'd reported
becoming dependent on pot by age 18 showed a drop in IQ score between
ages 13 and 38. The findings suggest pot is harmful to the adolescent
brain, the researchers said.
Not so fast, says an analysis published online Monday by the Proceedings of the National Academy of Sciences.
Ole
Rogeberg of the Ragnar Frisch Center for Economic Research in Oslo,
says the IQ trend might have nothing to do with pot. Rather, it may have
emerged from differences among the study participants in socioeconomic
status, or SES, which involves factors like income, education and
occupation, he says.
He based his paper on a
computer simulation. It traced what would happen to IQ scores over time
if they were affected by differences in SES in ways suggested by other
research, but not by smoking marijuana. He found patterns that looked
just like what the Duke study found.
In an
interview, Rogeberg said he's not claiming that his alternative
explanation is definitely right, just that the methods and evidence in
the original study aren't enough to rule it out. He suggested further
analyses the researchers could do.
The Duke
scientists, who learned of Rogeberg's analysis late last week, say they
conducted new statistical tests to assess his proposed explanation.
Their verdict: It's wrong. Rogeberg says they need to do still more
work to truly rule it out.
Experts unconnected
to the two papers said the Rogeberg paper doesn't overturn the original
study. It "raises some interesting points and possibilities," but
provides "speculation" rather than new data based on real people, said
Dr. Duncan Clark, who studies alcohol and drug use in adolescents at the
University of Pittsburgh.
Dr. Nora Volkow,
director of the National Institute on Drug Abuse, said observational
studies of people like the Duke work can't definitively demonstrate that
marijuana cause irreversible effects on the brain. In an email, she
said Rogeberg's paper "looks sound" but doesn't prove that his
alternative explanation is correct.
Copyright 2013 by The Assoicated Press. All rights reserved.
