A report that suggests regular marijuana smoking during the teen years can lead to a long-term drop in IQ has been challenged by a paper that says that the statistical analysis behind the conclusion is flawed. The original study, which was 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 suggested that pot is harmful to the adolescent brain, the researchers said. Ole Rogeberg of the Ragnar Frisch Center for Economic Research in Oslo, said that the IQ trend might have nothing to do with pot, the Huffington Post reported. Rather, it may have emerged from differences among the study participants in socioeconomic status, or SES, which involved factors like income, education and occupation, he said. Rogeberg based his paper on a computer simulation, which 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. He 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. The paper has been published online on the Proceedings of the National Academy of Sciences. ANI