IQ is a relative measure, pretending to be the % of the normal level of a individual in a similar age, in resumen: Relative to what or whom?. Intelligence isn't medible directly, because it isn't a objective value, depending on the test, it isn't only the capability to solve problems, it's also the capability to interact with others, emphatic capability, kinetic capabilities. Eg. Newton maybe was a genios with an IQ of 190 in Science and Math, but in interactions with others stupid like a brick (Asperger syndrom)
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IQ as a measuring metric was debunked by one of the Canadian universities a number of years back.
Just like calories don't technically exist in humans. It's useful even though it's not completely accurate
Life is filled with lots of these approximate lies that are more useful then not
Everything you said was true, but there's a small group of shortcuts that are very harmful when misused. "IQ", "GDP", and many others are routinely used in bad ways, and are therefore not 'more useful than not'. So overall, correct, but specific usage of these distinct meanings are very harmful, and always worth scrutinizing.
In German there's a saying "Wer misst, misst Mist."
"If you measure, you measure garbage."
The point here is that measurements often don't measure the exact thing you are looking for, but something adjacent to it. And measuring the wrong thing ends up optimizing that wrong thing instead of what you really want to optimize.