Several negative reviews of the book have been published in the scholarly literature. Susan Barnett and Wendy Williams wrote that "we see an edifice built on layer upon layer of arbitrary assumptions and selective data manipulation. The data on which the entire book is based are of questionable validity and are used in ways that cannot be justified." They also wrote that cross country comparisons are "virtually meaningless."[6]
Richardson (2004) argued, citing the Flynn effect as the best evidence, that Lynn has the causal connection backwards and suggested that "the average IQ of a population is simply an index of the size of its middle class, both of which are results of industrial development". The review concludes that "This is not so much science, then, as a social crusade."[3] A review by MR Palairet criticized the book's methodology, particularly the imprecise estimates of GDP and the fact that IQ data was only available for 81 of the 185 countries studied. However, the review concluded that the book was "a powerful challenge to economic historians and development economists", and that its conclusions were in great need of further analysis.[7]