[btilly]

We have evidence of causation here. Research during the 1960s shows that IQ tests do a better job of predicting future job performance than other measures, such as interviews. As a result, many companies began to use IQ tests for hiring.

This ended with https://en.wikipedia.org/wiki/Griggs_v._Duke_Power_Co.. The fact that IQ tests resulted in hiring whites at a higher rate than blacks was deemed a violation of the Civil Rights Act and so the practice was banned. The correlation remains true, but it is illegal to hire based on IQ.