> Of course it does, it doesn't need to be studied; No, public health mandates are not something you derive from first principles, but from actual observationa

> Of course it does, it doesn't need to be studied; No, public health mandates are not something you derive from first principles, but from actual observational data about the effectiveness of interventions. It's like the difference between a drug being effective in vitro rather than in vivo. There are many confounding factors and side effects that need to be understood, so it is irresponsible to skip directly from the in vitro study to mass distribution of an intervention. To help illustrate this point, let's assume that wearing the N95 masks reduces the likelihood of getting infected by some fraction, but not enough to drive the reproduction rate down below 1 (which is certainly the case). Say you only get from 2.0 to 1.8. Therefore unless this difference is the key to overwhelming hospitals, it should make no difference to death rates. However: Those who have lung disease (14% of the population) are less likely to wear these masks because it makes breathing more difficult for them, so they will become differentially more likely to catch the disease as a result of the healthy population wearing the masks than if no one was wearing the masks. But since herd immunity will be reached anyway (just at a later time), this intervention may result in an increase in deaths as the population of infected people will have a greater share of those with lung disease than if no one wore the masks. Now, is the scenario I laid out true? Well, we don't really know what herd immunity is here, and we don't know whether differential rates of compliance are big enough, which is why you have to study it. You always have to study. You don't go from a thought experiment to an intervention without study, because there are always confounding factors that can reverse your thought experiment once the intervention is applied in the real world. This is actually historically interesting, because it was the ineffectiveness of masks during the 1918 flu epidemic that was one of the major findings of public health, distinguishing it as a separate field from immunology. E.g. everyone assumed you needed to wear masks, but ex-post studies showed this made no difference for death rates in the 1918 pandemic. Now, I'm not saying that the 1918 data is decisive here, because they didn't have N95 masks then, but still use of the masks they did have was considered a best practice by immunologists, so it was still a shocking result how something that worked in the thought experiment could fail when deployed as an intervention. All of a sudden, people began to realize that "Yes, you need to study these things. First principles and logical deduction is not enough." That realization that public health is not immunology plus Aristotelian logic but is instead its own field -- that is the bedrock axiom of public health.