COUNTERFACTUALS
Does Omicron having lower fatality rate than Delta mean that it's milder?
Does a peak in cases during a mask mandate mean that masks do not work?
No. Let me explain it using counterfactuals
(short thread)
Example 1: Does Omicron having lower fatality rate than Delta mean it's milder?
Counterfactual: if Omicron was as severe as Delta, would its fatality rate be lower?
Answer: yes, bc of the below
Conclusion: Omicron's lower FR doesn't imply it's milder
twitter.com/nntaleb/status/1475125312484749312
Does it mean that we cannot conclude whether Omicron is milder than Delta?
No, we can. But we must control for the relevant variables. For example, studying Omicron’s IFR in people with no vaccine nor prior infection. (Studies that do say that Omicron is just as severe as Delta)
Example 2: does this chart mean masks do not work?
Counterfactual: if masks worked, would the chart look like the below?
Answer: yes (bc masks are not always worn and mandates are enacted when cases rise)
Conclusions: the chart below doesn't imply masks do not work
How would the chart look like if masks didn't work?
Same shape, just higher (dilated over the y-axis).
This means that just by looking at similar charts, we cannot say whether masks work.
(How can we say whether they work? Physics – laws, not models – and/or RCTs)
Example 3: does Sweden having had a smaller first wave compared to Italy mean that restrictions do not work?
Counterfactual: suppose on 1st March 2020, 🇸🇪 had 100 cases and 🇮🇹 10,000. Would Italy have a worst first wave?
Answer: yes. So, a worse wave doesn't inform on policy.
Example 4: hospitals showed normal Occupancy Rate so they aren't overwhelmed
Counterfactual: would overwhelmed hospitals show higher Occupancy Rates?
Answer: they'd keep OR semi-constant by cancelling elective surgeries
Conclusion: OR isn't a good proxy for overwhelming