[zeehio]

I would believe those results if they had published the methods (including everything they were correcting for, etc) BEFORE starting the data collection.

Otherwise I can argue that once you have all the data it is feasible to test many different combinations of variable corrections, age groupings, tattoo sizes, etc. until you find one scenario (the one you publish) with "statistical significance".

I had a quick glance at the article and the authors do not discuss any multiple testing correction method. The lack of such discussion makes me think that they were unaware of such problem and they tested multiple hypothesis until they found one "statistically significant". This is called cherry picking. https://xkcd.com/882/

I can think of two alternatives to the cherry picking hypothesis that might make me believe their conclusion will hold:

1. They had the statistical analysis plan decided from the beginning up to the smallest detail. They followed it by the book and they found the published result without exploring anything else, so there were no other hypothesis to correct for multiple testing for. This is feasible, but seeing the significance and effect size it seems this would be a very risky study design, since the effect size they see is rather small. Since it's so risky, I find it unlikely.

2. The result holds regardless of forcing minor variations to all those corrections. This means there would probably exist a simpler analysis plan, without so many corrections, that presents compatible results with the published plan. This is unlikely in my opinion, because if that were the case I would expect a simpler story in the paper, or a larger effect size.

Maybe an independent group of researchers believes in these results and decides to reproduce the study to confirm it. If this happens I hope they follow the same statistical analysis plan published in this paper, and I hope they can publish their findings in the same journal, even if they can't get a "statistical significance".