Last year a study done in New Zealand concluded teenagers who smoke marijuana had lower IQ scores. But a new analysis says that might not be the cause of a long-term drop in IQ. Statistical analysis may be why the conclusion is flawed.
The original study last August was conducted by researchers at Duke University and elsewhere. Researchers looked at more than 1,000 people who had been born in Dunedin, New Zealand. They tested the participants IQ at ages 13 and then at 18. They were asked about their marijuana use periodically through the ages of 13 and 18.
The researchers concluded that smoking pot caused a drop in IQ score for those between the ages of 13 and 38 who said they became dependent on smoking pot, according to Yahoo News. However, an analysis done by the Proceedings of the National Academy of Sciences said that it wasn’t pot that lowered the IQ scores but that factors related to economic class and home life may have caused the IQ drop.
The researchers who conducted the new analysis did not have access to the original data from the New Zealand teenagers. A labor economists at the Frisch Center in Norway, Ole Rogeberg used a computer simulation that, in theory, shows the same drop in IQ could be explained by socioeconomic factors that cause IQ-decreasing behaviors.
Rogeberg said, “The kinds of environments you are in do affect your IQ.” He added that good education and challenging jobs can boost intelligence, but “if people are pushed out or decide to move out of these kinds of arenas, they will tend to see an IQ decline, and they will also be the type of people who tend to take up cannabis smoking during adolescence,” according toLive Science.
The original researchers at Duke University said, in response to Rogeberg’s challenge of their conclusion, that they conducted a new analysis and found that IQ overall remained fairly stable. Additionally, they only used kids from middle-class families, therefore eliminating the effects of socioeconomic status.
But Rogeberg said those steps can’t rule out other factors as the cause for lower IQ. He said, “While interesting, the new analysis is not at all sufficient to address these concerns – but I look forward to seeing a fuller analysis in time.”