[hombre_fatal]

That's the midwit's causation vs correlation meme which is usually at play when an HNer uses both those words in a comment.

Observational research is how we know that smoking cigarettes causes health issues. We don't have 30 year RCTs on smokers. And there is no such thing as causation vs correlation. All we have are causal inferences draws from correlation.

Finally, when you suggest there are confounders, that's a causal claim. What confounders do you have in mind here, what standard of evidence do you need to accept them as confounders, and do they supersede the evidence we have for lead and IQ?

[giantg2]

"And there is no such thing as causation vs correlation. All we have are causal inferences draws from correlation."

A lot of it depends on how well the controls were done and what follow-up research was done. Thongs like identifying and confirming mechanisms of action are a huge difference between some basic correlation and claimed causation. In the case of exposures, you can work backwards - reduce blood levels and perform tests to see if functions return. That's a lot easier than identifying people before they meet the criteria. Although that's still possible, especially when dealing with certain vocational scenarios where tests can be performed before possible exposures.

[mint2]

“Reduce blood levels and see if functions return” so like reduce smoking to see if lung cancer go into remission? Why the assumption health effects are reversible?

[toast0]

You can certainly reduce smoking to see if lung capacity improves. I don't think it's reasonable to reduce smoking to see if that will cause an existing tumor to go into remission, for the same reason it's not reasonable to see if installing a blade guard on a saw will make a amputated finger reattach or regrow. The risk has manifested, and removing the risk factor is too late.

You'd need a large study to determine if stopping smoking reduces future risk of tumors; it's not something you can determine in a single person.

[giantg2]

"You'd need a large study to determine if stopping smoking reduces future risk of tumors; it's not something you can determine in a single person."

And they have done some studies that seem to prove the risk does decrease after cessation and continues to decrease over time.

[giantg2]

Not all health affects are reversible. Some reversals can be quite evident for acute symptoms, like arsenic. IQ reduction from lead appears to be permenant. Using your example of lung cancer... no, the cancer would not go into remission if established. However, there are studies showing lung cancer risk go down for smokers after they stop smoking, and generally the risk continues to decrease the more time has passed since they last smoked.

[coffeecat]

"Correlation does not imply causation" is a simple idea, but it truly cannot be emphasized enough. Establishing a correlation certainly does help to strengthen an already-compelling causal mechanism theory. Pulling high doses of carcinogen-filled particles into your lungs causes lung cancer? Sounds about right. Reduced IQ from exposure to a neurotoxin at levels significantly lower than that which produces clinical symptoms? Maybe, but I'd say the burden of evidence is higher on that one.

> Finally, when you suggest there are confounders, that's a causal claim. What confounders do you have in mind here, what standard of evidence do you need to accept them as confounders, and do they supersede the evidence we have for lead and IQ?

Dirt and dust ingestion, for which lead is a noisy metric. It's no accident that the correlation between lead and IQ is strongest at age 2. That's the age by which the smarter children have figured out that dust bunnies don't taste very good.