There has been alot of debate on whether hydroxychloroquine (HCQ) is effective in preventing or treating COVID-19. What got things started was a French study suggesting efficacy in lowering the viral load in patients with COVID-19 back in March 2020. We have learned alot since then and other studies have called into question both the efficacy and safety of HCQ in treating COVID-19.
The French study was a non-randomized study of 36 hospitalized people in which patients were recruited either into a treatment group or control (non-treatment) group. This was an observational study. Since then, there have been roughly 900 published studies in which the vast majority are observational studies. So whats the difference?
In an observational study, the effect of the drug being tested (in this case HCQ), is due to its true causal effect (lowering viral load or treating the infection) AND the characteristics of who was selected for treatment.
Whereas, in a randomized trial, because the selection is random, the effect is due solely to the true effect of the treatment. This is a much better type of study looking primarily at the effect of the drug treatment.
So if you are able to select the people in the treatment group, the researcher can tend to choose those that are younger, and who have fewer co-morbidities which is poised to do better than if the treatment was assigned randomly.
Observational studies are still good studies and should be used to design randomized studies. Randomized studies should then be used to guide therapy.
So the next time you are reading research about a new prevention or treatment for COVID-19, check to see if it is a randomized study. It will serve to be more reliable.
References: Randomized clinical trials