A correct indicative serology sample to determine IFR is based exactly proportionally to the areas where deaths occurred. If 80% of the deaths are in 25% of your zip codes then your sero sample should be populated 80% from those zip codes not 25%. NYC sero sample didn't do that.
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Replying to @12FreeBeer @GidMK
To calculate IFR off of the broad based NYC serology is nonsense. That sample isn't appropriately weighted to where deaths occurred. All of these "back of the envelope" IFR calcs overestimate IFR & in NYC its a significant overestimate given how high sero is in heavy hit areas.
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Replying to @12FreeBeer
Epidemiologically, that's basically nonsense. You would expect both the seropositivity and death rates to vary by suburb, due to demographic and other factors, and so weighting by seropositive tests would unnecessarily bias your final number
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Replying to @GidMK
It's math. If 100% of your deaths are in 10 neighborhoods representing 10% of your population, then sampling in the other 90% is useless. It's like including samples from Kansas when you're trying to figure out the IFR in Arizona. Your sero sample has to be where deaths occur.
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Replying to @12FreeBeer
Nope, that'd give you a totally useless estimate. The serosurveys should ideally be population representative and randomly sampled, otherwise all you're doing is picking a different bias for your sample
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Replying to @GidMK
Wrong. You take random broad demographic samples in the communities where people are dying & weight those samples based on community death proportion to figure out IFR & IFR by demographic. It's exactly how people who actually have to earn a living underwriting such risk do it.
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Replying to @12FreeBeer
Demographics absolutely, one of the weaknesses of current estimates is that they are not at least age-stratified. I think what you're describing is simply using smaller blocks for IFR - not entirely unjustified - not 'weighting' by suburb (which would be a bad idea)
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Replying to @GidMK
Yes, IFR by borough, neighborhood & apartment complex as NYC is very heterogeneous. Have to make sure all appropriately represented (it’s not in NYC sero study, sample is also WAY too small). Some apartment complexes (& all care homes) with outbreaks not even included in sample.
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Replying to @12FreeBeer
Sample definitely isn't way too small, it's far more about design than specifically large sample sizes. Some of the more robust epidemiological surveys in the US have only 10k participants total
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Replying to @GidMK
It’s way too small & narrow for NYC’s heterogeneity. Neighborhoods, apartment complexes & nursing homes w/ massive outbreaks & 50+% seroprevalence had ZERO representation in NYC sample. People who make livings underwriting this risk know it as do all the quants here. IFRs lower.
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Look, I'm not going to go over epidemiological sampling for you any more, it's a complex topic and there's only so much time in the world. Look it up sometime 
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Replying to @GidMK
I've seen enough bad math & analytics already from the epidemiological community. "Let's over represent low seroprevelance areas while excluding high seroprevelance areas from the sample." Classic! Just another epidemiological denominator disaster & more sloppy analytics.
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