> > Why? Probably because vitamin D is produced in the skin when we are in the sun. The more healthy subpopulation of any study will typically spend more time outside, so they will have higher vitamin D levels. But it’s (relative) health that causes higher vitamin D, not the other way around.
> You realise that you are proclaiming causality here?
Yes, with emphasis on the word probably. Just like I will happily proclaim that exercise probably lowers mortality.
> A RCT does not establish causality. That's essentially my point. A single study/experiment never proofs causality. You need a theory to explain the causality and multiple studies that falsify other possible causality mechanisms. That has been done extensively for excercise and morbity/mortality, the current study just establishes that this also correlates in the bigger picture. So yes the study itself does not "proof" causality, it's just a piece in the bigger puzzle of causality.
The beauty of an end-to-end RCT is that it effectively neutralizes other possible causality mechanisms. You do not seem to appreciate this. My impression is that your reasoning is more in line with evidence based medicine (EBM), rather than the hypothetico-deductive method that I personally subscribe to. In my way of thinking there will never be definitive “proof” of causality, but I will happily take a drug that has gone through sufficiently powerful RCTs that failed to prove its ineffectiveness (and harm).
> You realise that you are proclaiming causality here?
Yes, with emphasis on the word probably. Just like I will happily proclaim that exercise probably lowers mortality.
> A RCT does not establish causality. That's essentially my point. A single study/experiment never proofs causality. You need a theory to explain the causality and multiple studies that falsify other possible causality mechanisms. That has been done extensively for excercise and morbity/mortality, the current study just establishes that this also correlates in the bigger picture. So yes the study itself does not "proof" causality, it's just a piece in the bigger puzzle of causality.
The beauty of an end-to-end RCT is that it effectively neutralizes other possible causality mechanisms. You do not seem to appreciate this. My impression is that your reasoning is more in line with evidence based medicine (EBM), rather than the hypothetico-deductive method that I personally subscribe to. In my way of thinking there will never be definitive “proof” of causality, but I will happily take a drug that has gone through sufficiently powerful RCTs that failed to prove its ineffectiveness (and harm).