[refulgentis]

I'm not sure "people with negative msgs in tattoos died 14 years earlier" sheds light for me on the TFA.

TFA has a more direct, physical, concern - it starts from a well-known, that tattoo ink ends up in lymph nodes, and it does a statistical analysis showing there's a significant statistical result in lymphoma occurence.

I think people with negative tattoos dying younger reduces the # of people with tattoos who get lymphoma, as they have less ink-in-lymph-nodes years.

[marcosdumay]

It shows the existence of some very strong confounding mechanisms.

[refulgentis]

There's certainly plenty of those! :)

I doubt they intended to communicate something that general, and if they did, I doubt they meant to pick one that would reinforce the conclusion.