That "correlation is not causation" is obvious to researchers but they cannot pick the treatments in their study, so instead what they have to do is try to remo

That "correlation is not causation" is obvious to researchers but they cannot pick the treatments in their study, so instead what they have to do is try to remove confounding factors instead. E.g. "people that play chess may be smarter than those that knit so we controlled for education level and IQ", and so on. Whether the study is convincing in the end will depend partly on how well the researchers covered their bases and dealt with the defeaters raised during the peer review process and before it. It is a standard issue with observational studies.