What is the proper interpretation of the Minnesota Transracial Adoption Study?

The Minnesota Transracial Adoption Study was a long project dedicated to directly measuring the influence of shared environment on the racial gaps in intelligence. The original paper about it came out in 1976 and the authors hypothesized that socialization in favorable environments would significantly reduce the racial gap in IQ (Scarr and Weinberg, 1976). At that point, the data did suggest an environmentalist hypothesis regarding race differences, however it was revisited by the authors in 1992, an event which caused much more controversy regarding the results. While the authors still supported an environmentalist position (Weinberg et al., 1992), their data brought a number of replies. In this post, I am going to summarize the main arguments used by the authors and review the replies as well as the authors’ responses to those replies.

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Percent Black and Crime

An interesting predictor of local crime rates is the percent of the region examined that is black. Some may point to this and say that this is a result of discrimination. This is unlikely, as Rubenstein (2016) finds “Victim and witness surveys show that police arrest violent criminals in close proportion to the rates at which criminals of different races commit violent crimes.” Other reasons could include socioeconomic standards in the neighborhood, race differences in IQ, and underlying genetic differences in crime-committing-variables (aggression, ASB, etc.). Whatever the cause, the evidence for the association is documented in this blog post.

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Response to Richardson and Norgate (2015): “Does IQ Really Predict Job Performance?”

Ken Richardson is a figure in the psychometric world who has made some pretty bold claims about g, heritability, and IQ testing as a whole. Out of his many (flawed) works, there is one in particular I wished to respond to. Richardson and Norgate (2015) argue that the correlation between IQ and job performance is, at best, greatly overestimated by the pro-IQ side (figures such as Ian Deary, Richard Haier, Arthur Jensen, and most notably in the job performance debate, Frank Schmidt and John Hunter) and at worst, entirely useless. Do their arguments hold up?

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