They did not figure it out, the fact that IQ tests as we know today could predict performance in a wide array of tasks was basically an observation coming out o

They did not figure it out, the fact that IQ tests as we know today could predict performance in a wide array of tasks was basically an observation coming out of the data. Many other types of tests were tried for this, because being able to predict people's performances has extremely important implications, but the ones that did not predict anything were forgotten, while the ones that worked, like the current generation of IQ tests, became widely accepted (despite being attacked every now and then by a few researches, as in this case - which is a good thing as we need to make sure our current theories are as good as they can be).