Keep in mind that they aren't saying that their data doesn't say that people not given vitamin D supplements were 10x more likely to die. Instead that people co

Keep in mind that they aren't saying that their data doesn't say that people not given vitamin D supplements were 10x more likely to die. Instead that people coming in with a deficiency already were 10x more likely to die. Imagine if you had two groups. Group A runs for 1 hour a day outside. The group B is confined to their beds in a nursing home. Group B is going to have a vitamin D deficiency compared to group A. Group A is also much more likely to survive Covid. However, this wouldn't give you any evidence that vitamin D is the cause of better survival rates. You should assume that it might just be an indicator of better health over all unless you can find some way to control for all the other health factors.