1/ On the need for RCTs for all evidence before it is believable at all.
Prominent ppl from the health side say this often, e.g.:
Without an RCT, they don’t really believe anything. Let me offer some thoughts.
Prominent ppl from the health side say this often, e.g.:
Without an RCT, they don’t really believe anything. Let me offer some thoughts.
2/ First of all, what is an RCT?
Randomized Control Trial, you e.g. give 100 HEPA filter units to 100 households, they randomly have a working filter or not. Then you swap and redo. Households and technicians don't know if real or not. Measure outcomes, defeat placebo effect.
Randomized Control Trial, you e.g. give 100 HEPA filter units to 100 households, they randomly have a working filter or not. Then you swap and redo. Households and technicians don't know if real or not. Measure outcomes, defeat placebo effect.
3/ Fully empirical. Clearly critical for very complex matters such as new cancer drug or vaccine (w/ possibly serious side effects), extraordinary web of biological interactions. Only empirical demonstration is convincing before making critically important decision to use or not
4/ Because in medicine there are many such empirical hyper-complex problems, it seems that they have extended this thinking that "RCTs is the only way to prove things" to **everything**
5/ Meet physics & engineering: based on “first principles thinking”. Know eg Newton’s laws, figure out new things, relate them to Newton’s laws.
Combined body of knowledge allows to make good predictions for new situations. Still need to test, but can make v high quality pred.
Combined body of knowledge allows to make good predictions for new situations. Still need to test, but can make v high quality pred.
6/ First-principles- based thinking proven over and over. That’s what got astronauts on the moon and many other science, tech, engineering achievements.
7/ On to question about whether to recommend HEPA filters in schools. Most ppl paying attention agree that aerosols contribute significantly to COVID-19 spread. Droplets zero evidence. Yours truly estimates aerosols 75% in community, pre/asymptomatic () 
8/ Now, once one accepts that aerosol transmission is at least likely, we can use first-principles thinking from them on. We know a lot about aerosols move in air, we know how they can be removed by e.g. HEPA filters.
9/ Many yrs of experiments on how filtering removes aerosols of different sizes. Can predict how quickly to good approx. Lots of details to fine tune. But no need for RCT before deploying.
Like concluding that dehydrated patient needs fluids (I hope that didn’t need an RCT??)
Like concluding that dehydrated patient needs fluids (I hope that didn’t need an RCT??)
10/ Demanding RCTs for HEPA filters before starting large scale intervention, with time so short before schools start, makes no sense.
Like: "We know that water falls downstream in comm. But in a hospital, it may not. We need an RCT to show that before we can install drains!"
Like: "We know that water falls downstream in comm. But in a hospital, it may not. We need an RCT to show that before we can install drains!"
@samhorwich @eliowa, your take?
To be clear, I am not opposed to doing HEPA RCTs. I hope they are done.
But can massively deploy HEPA before we have results, and be confident on significant benefit.
But can massively deploy HEPA before we have results, and be confident on significant benefit.
BTW, HEPA in all US schools: $1 billion! Very difficult for school districts, but **peanuts* for Federal Government, in context of pandemic stimulus. Should invoke Defense Production Act
