[gwern]

This is a Swedish study, so what might be possible is using the population registry to contact siblings of the cancer patients to ask about traits like tattooing and then their health data would already be in Swedish system and linkable. This would control for a lot of the relevant confounders.

[tempestn]

Though not those related to people's choice to get tattoos.

[esperent]

Tattoos are so common these days that I'm not sure you can say much about a person just because they have tattoos.

[tempestn]

Any given person, for sure. In aggregate though I bet you'd find correlations.

[robin_reala]

Not sure you could in Sweden. Stats[1] show 21% tattoo prevalance in Sweden compared to 12% in the EU in general.

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10163470/

[tyre]

they are statistically cooler

[rightbyte]

Which is a strong confounding factor ...

"Sharing traits common in motor cycle gangs increases risk of cancer - new study"

[gwern]

No, it would control for a lot of those factors. Things like impulsivity, sexuality, sensation-seeking etc. All very heritable or family-level. If you ever find any correlations reported for tattoos between family members, it's gonna look like everything else: steeply increasing with relatedness.