My recent posts have focussed on IQ and the differences between a gap in IQ test results and a gap in general intelligence or g. The contemporary difference between white and Black racial mean IQ is about 10 points. For every IQ test subject, including all white subjects and all Black subjects, some portion of that IQ score represents a measurement of g. However, there are good reasons to think that the proportion of the IQ score that measures g will be different among white people from the proportion measuring g among Black people. While I don’t think that motivation is different enough between racial groups to explain the mean IQ score gap, it’s very interesting and relevant to note that placebo effects that are likely due entirely or almost entirely to motivation effects (primarily a combination of arousal effects and attention effects) can on their own generate a 10 point difference in mean IQ test scores. The Proceedings of the National Academy of Sciences (in this case, the “nation” is the USA) has the lowdown.

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