Now we see that the so-called research that the opponents of marijuana legalization were touting as "definitive proof" that marijuana use damages teen brains has been revealed as bogus with flawed methodology and deceptive causal inference drawn from premature evidence. The review of the pseudo-scientific deceit found that "the true effect (of marijuana on teen cognition) could be zero." So how did the original research team come up with such flawed results? By tailoring the study's parameters and subject population and protocol to give them the results they wanted. Why? Because bad science on marijuana gets excellent funding. With the turn in public opinion and the move by the first two states to legalize marijuana, be prepared to hear more and more desperate assertions drawn from bogus research in a pitiful effort to hide the truth about marijuana and how it benefits human health. 2013 Jan 14. [Epub ahead of print]
Correlations between cannabis use and IQ change in the Dunedin cohort are consistent with confounding from socioeconomic status.
Does cannabis use have substantial and permanent effects on neuropsychological functioning? Renewed and intense attention to the issue has followed recent research on the Dunedin cohort, which found a positive association between, on the one hand, adolescent-onset cannabis use and dependence and, on the other hand, a decline in IQ from childhood to adulthood [Meier et al. (2012) Proc Natl Acad Sci USA 109(40):E2657-E2664]. The association is given a causal interpretation by the authors, but existing research suggests an alternative confounding model based on time-varying effects of socioeconomic status on IQ. A simulation of the confounding model reproduces the reported associations from the Dunedin cohort, suggesting that the causal effects estimated in Meier et al. are likely to be overestimates, and that the true effect could be zero. Further analyses of the Dunedin cohort are proposed to distinguish between the competing interpretations. 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.