Several of those authors are discredited as frauds. Rushton was paid to tailor results to support a conclusion, and deliberately chose sample groups to produce the desired result.
The studies are meta-analyses, using data sets on different ethnic and racial groups acquired at different points in time in different locations. Some of them are meta-analyses
of meta-analyses. No attempt has been made to control for... anything, aside from body mass. They aren't comparing apples to apples -- caucasian data comes from students at a university measured using one technique, while the data on black folks comes from a study separated by thousands of miles and decades in time. It's deliberate selection bias. At least if the cohorts were drawn from socio-economically-similar populations inferences could be drawn. We might only have learned how different groups respond to the same environmental stressors, but at least we'd have actually learned something. As it is, basically all we've learned is that yes, p-hacking works when you want to fabricate support.
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