Thanks for your feedback, in fact correlation is not causation and we must be very careful about self-selection effects. This is not a self-selection effect but still a correlation/​causation enigma that I found interesting in recent times: high vitamin D levels were found to be heavily anticorrelated with severe COVID in observational studies, but people of old age are both sensible to severe COVID and have lower vitamin D than average, not only that but people with a healthy lifestyle of many outdoor walks also have higher vitamin D! Is this causation, correlation or both? There is a very interesting article about this on Astral Codex 10 (COVID/​Vitamin D, Much More Than You Wanted To Know)
Thanks for your feedback, in fact correlation is not causation and we must be very careful about self-selection effects. This is not a self-selection effect but still a correlation/​causation enigma that I found interesting in recent times: high vitamin D levels were found to be heavily anticorrelated with severe COVID in observational studies, but people of old age are both sensible to severe COVID and have lower vitamin D than average, not only that but people with a healthy lifestyle of many outdoor walks also have higher vitamin D! Is this causation, correlation or both? There is a very interesting article about this on Astral Codex 10 (COVID/​Vitamin D, Much More Than You Wanted To Know)