system
Given the following post, respond as if you're commenting on Reddit:
human
Is IQ a useful measurement?

So a buddy and I got into a debate IQ on whether IQ is a useful measurement (I know useful is an extremely general term). Both of us are not psychologists, (we are engineers). I've always understood IQ as a an extremely general and misunderstood statistic that had limited applications, but was given extreme importance (Similar to BMI vs Body Fat Percentage). He disagreed and shut it down by saying I didn't psychology.

I have a STRONG backing in math, specifically in Statistics (was the only stat tutor at my first college for a year). So I tend to sift through a lot of stuff if I'm not satisfied with confidence intervals or if I think the p-value is based on subjective criteria, etc. I just wondered if there are any perspectives that would change my mind and what other people think.

Edit: Great answers so far. I should add more to what the useful portion implies. It was for determining intelligence and as a recruitment tool for schools amd businesses.
gpt
It might help to have a quick definition of IQ: all measurable cognitive abilities (from the ability to solve logic puzzles to pure reaction time) are correlated with one another. Someone who does one mental task well is likely to also do other mental tasks well. What we call IQ is just a general estimate of a person's cognitive ability across a variety of tasks.

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As you mention in your post, the answer to your question depends on what you mean by 'useful.' You need an IQ test to validly diagnose a whole variety of neurocognitive disorders (learning disorders, intellectual disability, ADHD, etc.), and it can be helpful when doing other psychological assessments as well. IQ is also interesting in that it correlates with all kinds of positive outcomes. That is, people with higher IQ tend to be healthier and better educated, they tend to commit less crime, and they tend to make more money. Whether that's a useful thing to know depends on what you're trying to do or learn.