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Comment by vintermann | Hacker News Reader

It's a good tool if you want to rank people, it's a bad tool if you want to help people. IQ tests couldn't (and can't) even detect dyslexia, a specific disability which you can get help with, which was known even in Terman's time. IQ tests by design throw out all information which could complicate ranking people. If your goal is to help, why would you measure people with a tool which can't tell the difference between dyslexia and concussion?

IQ tests have been revised several times to address things like that, like that they "unfairly" penalize dyslexia, or that they had lots of questions which were easier for people of specific social backgrounds. Every time they were, they naturally became less "predictive", since both dyslexia and not belonging to the California white upper middle class give you pretty obvious disadvantages in life outcomes.

So don't waste time on IQ, and don't waste time on other academic culture war BS either.

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Wait, this is the opposite of reality. IQ is in fact a useful tool (in a battery of other tools) for helping diagnose cognitive deficits and learning disabilities. That's what it's good for: as a clinical tool. It's in fact terrible for ranking people.

Well that's what it was used for! Do your history homework, mr. clinician!

Tell me then, if someone scored low on a text-based IQ test and that's all you know, how do you tell if it was caused by dyslexia or concussion? I guess you break out that "battery of other tools"? What does IQ tests give you that those other tools don't give better?

Oh, I know one. An excuse to write someone off as simply stupid. An excuse to _stop looking_ for the things which might have helped them. Which is what it was historically used for.

If you can’t study IQ how do you demonstrate that lead poisoning causes reduced intelligence?

The research to ban lead in fuel relied on measuring IQ and measuring lead exposure, then showing a correlation between the two.

At the population level IQ is a very useful tool.

IQ is a very bad tool for measuring populations. That's because IQ is definitionally designed to force a population to adhere a particular metric: a bell curve distribution, with the median at 100 and the standard deviation of 10. Whatever the thing you're measuring is--and there's good reason to think it's not "intelligence"--you're crunching and distorting that measurement to get the number at the end of it to force the population to adhere to a standard distribution.

We don't have a good model of what intelligence is. But since IQ studies are fairly common, there's a lot of data collected that uses IQ, and since it IQ looks vaguely like "intelligence," a lot of researchers who are motivated to find reasons to declare particular people intelligent or unintelligent are more than happy to use that data to support their claims.

Did you even read my comment?

Answer this question:

> If you can’t study IQ how do you demonstrate that lead poisoning causes reduced intelligence?

The answer to that question should be blindingly obvious: you don't.

It should be clearly evident that trying to use IQ to establish that "<insert ethnic group here> are stupid" is bad science. It's the same sort of science to establish that "<insert environmental factor here> causes stupidity," so we also need to reject it even if the environmental factor is clearly something problematic. The problem isn't the conclusion, it's the methodology.

So do you reject that lead poisoning causes stupidity because it is unethical to measure intelligence?

It’s a good thing that measuring IQ enabled us to discover that trace amounts of lead in the environment causes reduced intelligence. That was a key piece of data for banning lead in fuel. The loss of IQ points happens to all kids living in cities, rich and poor. Rich powerful people didn’t want their kids made stupid by lead in the air.

I think that removing lead from paint and fuel has greatly improved the lives of billions of people.

No, we knew lead was bad. We knew what heavy metal poisoning looked like, we knew lead caused heavy metal poisoning. We knew of a hell of a lot more concrete effects than average lower scores on IQ tests.

> The loss of IQ points happens to all kids living in cities

No, it didn't. The reduced test scores happened _on average_.

I won't rule out that what you said is correct, in that it may well be the fear that "my child may lose 1-5 IQ points!" helped get lead banned, but if so, that's an indictment of society.

I agree with half of this argument but think you're taking it too far when you reject IQ testing as an epidemiological tool. It's not dispositive. It's statistically ill fitted as a ranking tool, for the reasons you stated, and the fact that it's not reliable across its whole range, and test-test reliability issues, &c. But like, "you can use it as an indicator for environmental causes of cognitive harm" is actually a valid argument, I think?

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