Hacker News

points by sjducb 15 hours ago | 0 comments

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.

[–] jcranmer 15 hours ago

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.

[–] sjducb 14 hours ago

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?

[–] jcranmer 12 hours ago

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.

[–] sjducb 11 hours ago

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.

[–] vintermann 10 hours ago

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.

[–] tptacek 11 hours ago

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?