Anytime you see a highly-publicized study that claims to have absolute proof that marijuana is harmful, be suspicious, very suspicious. There are hundreds of millions of dollars available from the federal government for researchers who seek to find damage caused by regular marijuana use. Some are honest scientists (like Dr. Donald Tashkin) who do research to find harm and instead find benefits which they report without self-censorship while others are what I term "researchstitutes" who work to support an agenda not the free discovery of knowledge. They tailor study protocols and select patient populations in order to have the best chance of producing dire results, and yet, time after time they come up with data that indicates benefits. It is almost certain that many of these misfires have never seen the light of day because as one investigator stated, you don't get funding to continue studies which show benefits. Upon closer investigation, the scary conclusions are frequently discredited, as we apparently see here. Thank goodness for honest scientists. Marijuana Study Tying Teens' Pot Use To I.Q. Drop Is Flawed, New Paper Suggests
By MALCOLM RITTER 01/14/13 03:47 PM ET EST AP
NEW YORK — 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.