Tattoos and piercing. I haven’t found any evidence that this relates to intelligence or even creativity. On the other hand, what underlying factor of openness would it be an indication of?
I have. A long time ago, I tried to find a study of this. The only meaningful study I found was a small study of Croatian veterans:
Pozgain, I., Barkic, J., Filakovic, P., & Koic, O. (2004). Tattoo and personality traits in Croatian veterans. Yonsei medical journal, 45, 300-305.
The study has N≈100 and found a difference in IQ scores of about 5 IQ. Not very convincing.
In a still unpublished project, we scraped public data from OKCupid. We did this over several months, so the dataset has about N=70k. The dataset contains the public questions and users’ public answers to them, as well as profile information. Each question is multiple choice with 2 to 4 options.
Some of the questions can be used to make a rudimentary cognitive test. with 3-5 items that has reasonable sample size. This can then be used to calculate a mean cognitive score by answer category to all questions. Plots of the relevant questions are shown below. For interpretation, the SD of cognitive score is about 1, so the differences can be thought of as d values. There is some selection for cognitive ability (OKCupid is a more serious dating site mainly used by college students and graduates), so probably population-wide results would be a bit stronger in general. Worse, this selection gets stronger as the sample size decreases because smarter people tend to answer more questions. The effect is fairly small tho.