Pubdate: Tue, 15 Jan 2013
Source: Daily Freeman (Kingston, NY)
Copyright: 2013 Daily Freeman
Contact:  http://www.dailyfreeman.com/
Details: http://www.mapinc.org/media/3269
Note: from the Associated Press

LINK BETWEEN MARIJUANA, IQ CHALLENGED

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 author of the new paper says pot might not have anything to do
with the mental decline seen in the original study, and that other
factors may be to blame.

The original study 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.

Participants who said they were dependent on pot by age 18 showed a
drop in IQ score between ages 13 and 38, according to researchers at
Duke University and elsewhere. Their report, which got wide attention
last August, suggested pot is harmful to the adolescent brain.

Not so fast, says the new 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 emerged from differences among the
study participants in socioeconomic factors like income, education and
occupation.

He based his paper on a computer simulation. Drawing on results of
earlier research, It traced the potential effects of those
socioeconomic factors on IQ. He found patterns that looked just like
what the Duke study found for smoking marijuana.

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 with their data.

The Duke scientists, who learned of Rogeberg's paper late last week,
say they conducted new statistical tests that ruled out his
explanation.

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 causes 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 either.
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MAP posted-by: Jo-D