There is no way to know 20% of COVID infectees require hospitalization until we know the number of infectees. The figure you are using is a fraction of people with serious enough symptoms to go to the doctor - and no doubt some of those people go to the doctor on minor symptoms.
-- but most of our lives are shaped by speculation. How many eggs to get for next week --
Or when to buy toilet paper. All those decisions are based on experience. We have a fair handle on repeat/predicablt events. What is the household rate of egg consumption? Milk? How much gasoline do you consume in a month? How far is your commute and how many days a year do you go to work? Sure, there is some uncertaintly there, but not much.
How much uncertainty is there in "20% of people who become infected with COVID will require hospitalization"?
“There is no way to know 20% of COVID infectees require hospitalization until we know the number of infectees.”
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Those are confirmed cases, And as you noted, we have no way of knowing how many people aren’t infected. That’s getting into a “proving a negative” type of area.
“How much uncertainty is there in “20% of people who become infected with COVID will require hospitalization”?”
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I imagine you can just use “of all confirmed cases”, if you prefer, to be more semantically accurate. Doesn’t change the numbers, tho. ::shrug::