"Usually all the basic concerns have been accounted for in the actual study." Fair enough ... but there could be simple and nuanced elements that they didn't o

"Usually all the basic concerns have been accounted for in the actual study." Fair enough ... but there could be simple and nuanced elements that they didn't or couldn't measure. For example: maybe Sauna dwellers are far more socially active than others? Social interaction is maybe they driver of longevity, the sauna may simply be a part of that process. Anyhow, just a crude example ... but I'd suggest it's very hard for researchers to rule out most such things.