4 ms·

Ignore the people telling you it's 2-3%. The case fatality ratio is between 9 and 56% according to proper epidemiological methods, such as using the formula "de

by mrb 7y ago

Ignore the people telling you it's 2-3%. The case fatality ratio is between 9 and 56% according to proper epidemiological methods, such as using the formula "deaths / (deaths + recoveries)": https://mobile.twitter.com/zorinaq/status/1222427708723879936 https://mobile.twitter.com/zorinaq/status/122242770872387993... Disclosure: no I'm not an epidemiologist. But for a reference to a paper by actual epidemiologists see https://pdfs.semanticscholar.org/ebf2/48c9fc0a1a23d1778b94083319aa995e34f4.pdf https://pdfs.semanticscholar.org/ebf2/48c9fc0a1a23d1778b9408... section Simple Estimators, specifically this formula: e₂(s)=D(s)/{D(s)+R(s)} which is: deaths / (deaths + recoveries) The paper concludes: "The second simple estimate based on the ratio of deaths of those for whom the outcome is known, e₂, is reasonable at most points in the epidemic" ie. produces a good estimate of the eventual observed case fatality rate (in fact in their example it slightly underestimates the actual case fatality rate)

baq 7y ago
couldn't believe these numbers, read the link. correctness is obvious in retrospect, numbers are trivial to calculate by hand by just looking at daily data. still can't believe them.
- mrb 7y ago
  "Just looking at daily data" is your mistake. Essentially, it takes N days for the virus to kill, so deaths will lag confirmed cases by N days, and thus the calculated case fatality rate using this method is incorrect. This is why epidemiologists call it a "naïve esimator" (see section 3.1 in https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4540071/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4540071/).
colinmegill 7y ago
That's you touting your own feed, and you don't appear to be an epi scientist
- mrb 7y ago
  I'm just applying the work of epi scientists. I'd love to get feedback from one. Your comment isn't useful.
  - Fomite 7y ago
    Given you're posting on Twitter, adding the #epitwitter will get you plenty of exposure to ID epidemiologists, myself included.
goblin89 7y ago
If hospitals err on safe side and do not report recoveries promptly (they probably have other business to deal with), applying this method at such early stage would not result in correct numbers, even supposing the virus is well-studied enough to tell when a patient has recovered.
- mrb 7y ago
  Agreed, when using the "deaths / (deaths + recoveries)" formula, recoveries being under-reported is possible and would skew the CFR upward. But also, if deaths are under-reported in the same proportion as recoveries, then it would not affect the CFR. I suppose one way to reduce uncertainty is to examine a cohort of patients and follow it meticulously. To do that, we can look at the 99-patient case study published in The Lancet yesterday: https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)30211-7/fulltext https://www.thelancet.com/journals/lancet/article/PIIS0140-6... 11 died, 31 were discharged, and 57 remain in the hospital. This suggests a CFR of 11/(11+31) = 26% The assumption epidemiologists make when they use this formula is that the 57 still in the hospital have the same chance of dying as those who already died in the hospital.
  - goblin89 7y ago
    Assigning 50% chance of death to any patient remaining in the hospital when calculating mortality rate would be nuts, I can only thank the epidemiologists for not publishing the number.
    - mrb 7y ago
      Not 50%, you misunderstand me. I edited my comment to clarify. What I meant is out of those who came out of the hospital (either dead or recovered), 26% died. So those remaining in the hospital are assumed to have a 26% chance of dying. Another way of looking at probabilities, out of the 57 patients left in the hospital: If 0 die (ie. all recover), the CFR is 11% (11 deads, 88 recovered) If 15 die (26% of 57 still hospitalized), the CFR is 26% (11+15=26 deads, 73 recovered) If 57 die, the CFR is 69% (11+57=68 deads, 31 recovered) So the CFR bounds are 11-69% and if the trend on remaining patients continue it should be 26%.
AlayaMatrix 7y ago
It taks longer time to confirm recoveries than death.

by mrb 7y ago

baq 7y ago

couldn't believe these numbers, read the link. correctness is obvious in retrospect, numbers are trivial to calculate by hand by just looking at daily data. still can't believe them.

mrb 7y ago
"Just looking at daily data" is your mistake. Essentially, it takes N days for the virus to kill, so deaths will lag confirmed cases by N days, and thus the calculated case fatality rate using this method is incorrect. This is why epidemiologists call it a "naïve esimator" (see section 3.1 in https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4540071/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4540071/).

colinmegill 7y ago

That's you touting your own feed, and you don't appear to be an epi scientist

mrb 7y ago
I'm just applying the work of epi scientists. I'd love to get feedback from one. Your comment isn't useful.
- Fomite 7y ago
  Given you're posting on Twitter, adding the #epitwitter will get you plenty of exposure to ID epidemiologists, myself included.

goblin89 7y ago

If hospitals err on safe side and do not report recoveries promptly (they probably have other business to deal with), applying this method at such early stage would not result in correct numbers, even supposing the virus is well-studied enough to tell when a patient has recovered.

mrb 7y ago
Agreed, when using the "deaths / (deaths + recoveries)" formula, recoveries being under-reported is possible and would skew the CFR upward. But also, if deaths are under-reported in the same proportion as recoveries, then it would not affect the CFR. I suppose one way to reduce uncertainty is to examine a cohort of patients and follow it meticulously. To do that, we can look at the 99-patient case study published in The Lancet yesterday: https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)30211-7/fulltext https://www.thelancet.com/journals/lancet/article/PIIS0140-6... 11 died, 31 were discharged, and 57 remain in the hospital. This suggests a CFR of 11/(11+31) = 26% The assumption epidemiologists make when they use this formula is that the 57 still in the hospital have the same chance of dying as those who already died in the hospital.
- goblin89 7y ago
  Assigning 50% chance of death to any patient remaining in the hospital when calculating mortality rate would be nuts, I can only thank the epidemiologists for not publishing the number.
  - mrb 7y ago
    Not 50%, you misunderstand me. I edited my comment to clarify. What I meant is out of those who came out of the hospital (either dead or recovered), 26% died. So those remaining in the hospital are assumed to have a 26% chance of dying. Another way of looking at probabilities, out of the 57 patients left in the hospital: If 0 die (ie. all recover), the CFR is 11% (11 deads, 88 recovered) If 15 die (26% of 57 still hospitalized), the CFR is 26% (11+15=26 deads, 73 recovered) If 57 die, the CFR is 69% (11+57=68 deads, 31 recovered) So the CFR bounds are 11-69% and if the trend on remaining patients continue it should be 26%.

AlayaMatrix 7y ago

It taks longer time to confirm recoveries than death.