Hydroxychlorquine has been in the news a lot as a possible treatment for Covid-19. The Ford Study which is an observational study showed an association with taking the treatment and doing better. Can we determine causation from this OBSERVATIONAL study? Watch the video below for Dr. Fauci's answer.
Here's an interesting article which highlights that we don't always get what we expect in experiments. It also lists a confounding variable that might explain the unexpected results.
"Oxford/AstraZeneca Covid vaccine 'dose error' explained", Michelle Roberts, BBC News online, November 2020