
Ask HN: How do you prove a particle causes a health symptom? - boldpandabear
How can one definitively prove that the presence of a certain particle in the body is also the cause of a certain symptom? How do we know if it’s correlation or true causation?
======
giantg2
It's pretty hard to definitely prove individual occurence medical issues. For
example, exposure to arsenic is known to increase risk of cancers. Even if you
biopsy the tissue and find arsenic, you can't say for certain that is the
cause - look at how some tobacco users live to 90 and never develop cancer,
even if it's rare. It would probably be enough evidence in a court of law.

Large scale case studies can be good evidence depending on the nature of the
particles being studied and how easy it is to control for other variables.

------
Foober223
I guess if you can observe the damaging mechanic at the cellular level that is
proof of causation. Rather than just statistical correlation.

All tests that just look for end results without understanding the mechanism
would be showing statistical correlation. But correlation is good info. In the
real world, you are going to be well off taking statistical correlation to
heart. The Romans knew asbestos was deadly long before there was any ability
to observe mechanics at the cellular level. All they had to go on was that
people covered in asbestos died horrific deaths.

------
helph67
I know it as a `double blind' test, where some subjects will be given the
substance being tested and others a placebo.

[https://en.wikipedia.org/wiki/Randomized_controlled_trial](https://en.wikipedia.org/wiki/Randomized_controlled_trial)

Just recently this was posted which complicates the issue!
[https://news.ycombinator.com/item?id=24075091](https://news.ycombinator.com/item?id=24075091)

