It should be noted that this paper was published in 2013, and that there have been some subsequent comments/criticisms of it. While the original paper is behind

It should be noted that this paper was published in 2013, and that there have been some subsequent comments/criticisms of it. While the original paper is behind a paywall (does anyone know of a place to read it?), this comment on the paper by Wicherts and Scholten raises questions about the study and analysis: http://science.sciencemag.org/content/342/6163/1169.4.full http://science.sciencemag.org/content/342/6163/1169.4.full >[...]We note that a highly relevant potential confound in the field study presented by Mani et al. is the possibility of retesting effects. The lack of any retesting effect in Mani et al.’s field study involving Indian farmers is clearly at odds with one of the more robust findings in the literature on cognitive testing (9). Retesting effects on the Raven’s tests are particularly profound among test-takers with little education (10). >Mani et al. go beyond the data by concluding that “The poor…are less capable not because of inherent traits, but because the very context of poverty…impedes cognitive capacity.” We note that the correlation between income and IQ also appears in longitudinal studies in which IQ was measured years before incomes (11). Further research is needed to fully grasp whether poverty indeed affects cognitive performance, as proposed by Mani et al., or whether the effect found in their experiments is a test artifact. [...] --- I had similar doubts when reading the Princeton press release (though of course my doubts are only based on hunches and not rigorous statistical analysis). The experiment testing farmers pre-harvest and post-harvest has the potential issue of retesting/learning effects, because they had the same participants take the test both before harvest and then later after harvest. If they end up seeing an increase in performance from pre-harvest to post-harvest, that could also be due to learning/familiarity with the test and not just from the independent variable of altered poverty. I would want to see a similar study done either with separate (large) groups of participants pre/post-harvest, or to repeat the test over several harvest cycles so we can see if there is an oscillating rise/fall as it goes pre/post/pre/post-harvest.