Ask HN: How do you prove a particle causes a health symptom?

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.

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.

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

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