Hydroxychloroquine lowers Covid-19 death rate, Henry Ford Health study finds
detroitnews.com
detroitnews.com
This is probably a good hospital with good staff and good equipment. Globally many hospitals are not so good.
There may be some involuntary selection of the patients. For example here in Argentina the retired people have a special health plan that include only some hospitals. That may change the population that goes to each hospital and change the expected death rate. Some hospitals get more rich patients. Some hospitals may get more athletes. It is very difficult to be sure, so you need a randomized control group.
The big question is, how well randomized are these, and what's the effect size - could be suspiciously small.
If it's not randomized at all, the results do not necessarily show the drug is good - just that it's given to healthier patients. You can try to reduce such artifact by considering matching reference subgroups.
Without the same inclusion criteria it's not a control group but a unrelated bunch of guys.
That's the reason why in RCTs treatment and control groups are split from the same pool - less need to make sure they are.
Just remember that the first study by Raoult claims to have a control group, but it's better described a a unrelated bunch of guys in another city. And there are other studies with similar tricks.
I have seen Hydroxychloroquine go from promising to helpful to not-helpful to damaging to promising again.
http://www.paulgraham.com/submarine.html
https://www.wsj.com/articles/covid-19-drug-remdesivir-to-cos...