There is a great Radiolab series about this: G. The IQ test is an effort to measure "general intelligence", or "G", but the test has had biases over time with regard to race.

The landmark study by Herb Needleman on the link between lead exposure and IQ only studied white children to reduce any doubts about the validity of its claims [1].

[1] https://www.wnycstudios.org/podcasts/radiolab/articles/g-pro...