The big problem with IQ is that it's horribly misapplied. It's a predictor for how you will do in education. That is all it was designed to do and all it has ever been validated for. It does that ok, not great but well enough to be statistically significant. It has some reasonable use in identifying extreme outliers (the roughly 5% of people more than 2 standard deviations from the mean) which is useful for getting the roughly 2.5% of people more than 2 standard deviations below the mean the additional resources and care they need. There are no other valid community uses for IQ and for the vast majority of people it's a meaningless number. It unfortunately found a place in pop culture and in business and government recruitment when realistically it's use should have always been limited to research and selective clinical/educational applications (identifying people that need extra resources). Mass testing is undisputably a waste of resources because of how little useful information it generates and the high risk of misuse of basically meaningless results of the 95% that are within the normal range.