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A second study, released today, provides a different interpretation of the data: The IQ changes in the different populations could be due to their socioeconomic status, not their pot use.
The study used data from the Dundin cohort, a group of more than 1,000 children born between April 1, 1972 and March 31, 1973 in Dundin, New Zealand. They are now 38, and still being studied.
There are two problems, according to Ole Rogeberg, who authored the new analysis. He writes: "First, these estimates are based on small numbers. Second, as noted by the researchers, reduced schooling could be part of the causal path by which cannabis use lowers IQ."
Other studies of this group of kids have found "that early-onset cannabis use is more common for those with
So, Rogeberg simulated how these factors could have caused the IQ drop that the original researchers saw. His analysis was published today, Jan 14, in the journal Proceedings Of The National Academy of Sciences. He found that most, if not all, of the effect seen in the original study could be accounted for by the low SES factor.
These kids with lower socioeconomic status are less likely to be put into intellectually challenging environments, which are part-and-parcel of an increasing IQ score throughout life. Though the original study, by Madeline Meier, et. al, claims to have controlled for socioeconomic standard, Rogenberg says his new analysis indicates that this could have created the link they found between IQ and weed use.
Rogeberg writes:
Although it would be too strong to say that the results have been discredited, the methodology is flawed and the causal inference drawn from the results premature.
Arran Frood, writing for Nature, talked to Meier. She says that Rogeberg's analysis is interesting, but suggest that their analysis could still be right. He writes:
In their original analysis, Meier says, she and her colleagues controlled for socioeconomic status and found that in all socioeconomic categories, the IQs of children who were not heavy users remained unchanged from adolescence to adulthood. Therefore, she says, socioeconomic status does not influence IQ decline.
All in all, it sounds like the link between teen pot use and IQ is still very questionable, so don't take the word of just one researcher.
Other recent studies on pot-using teens indicated that, compared to teens that use alcohol, their brains are less physically impacted by the drug. (To be fair, this study didn't test the teen's IQ, only the physical changes to the brain.)