Benjamin de Haas explains individual differences in eye movement patterns.
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Edited by Leslie Lars Iversen, University of Oxford, Oxford, United Kingdom, and approved December 7, 2012 (received for review September 8, 2012)
Abstract
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.
Footnotes
- ↵1E-mail: ole.rogeberg{at}frisch.uio.no.
Author contributions: O.R. designed research, performed research, contributed new reagents/analytic tools, analyzed data, and wrote the paper.
The author declares no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1215678110/-/DCSupplemental.
References
Cannabis use, IQ change, and socioeconomic status
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- Meier et al., 2012: Study Design and Methodological Issues
- Who Are the Adolescent-Onset Cannabis Users?
- What Are Counterfactual IQ-Trajectories for Those at Risk for High Cannabis Exposure?
- Indications of SES Confounding in the Meier et al. Study
- Comparing and Contrasting the Causal and Confounding Model
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