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I don't quite follow your point. My model assumed implicit knowledge that the virus originated somewhere in China, but not in Wuhan. Maybe I should have made th

I don't quite follow your point. My model assumed implicit knowledge that the virus originated somewhere in China, but not in Wuhan. Maybe I should have made that more explicit. We could change the model to not have any implicit assumption about location. Then instead of dividing by the population of China, we'd divide by the world population. The result should be the same, assuming we appropriately adjust our prior probability P(virus from WIV) to account for the fact that there are more BSL-4 facilities worldwide than in China.

roenxi 7y ago
Well, I'm not qualified to explain this so I'm probably wrong in the detail, but a sketch of the thinking: P(Came from WIV|Global Epidemic starts in Wuhan) ~= 97% However, P(Started Near a BSL Rated facility|Global Epidemic) is also high (not going to estimate it). But you have assumed that P(Global Epidemic starts in Wuhan) = 1; which is not true. P(Global Epidemic starts in Wuhan) is probably quite low and they got unlucky because it had to start somewhere. In this context, that assumption is tantamount to flipping a coin then saying "P(Heads) = 1". It isn't, P(Head) = 0.5 but it does happen sometimes. If we assume P(Global Epidemic starts in Wuhan) = 1 (because it did happen) then P(Came from WIV) is either 0 or 1, because it either did or didn't happen in the same way that the virus started in Wuhan.
- dlubarov 7y ago
  Hm, you're making sense otherwise but I just don't see where I assumed P(Global Epidemic starts in Wuhan) = 1 -- could you elaborate on that?
  - roenxi 7y ago
    Probably not; no. The best I can come up with is that probability is very sensitive to what you assume is happening to generate results. In this case, you're assuming that the WIV in particular is important which I suspect links the pandemic implicitly to Wuhan. That isn't a math error, but it is not going to give you a useful result. This isn't an error of logic so much as an error in scenario construction - it is ignoring possibility that the virus appeared near a random BSL rated facility, which is probably very high since a new virus would likely be detected first in dense urban centers where that sort of infrastructure tends to be. If the virus is likely to appear near a BSL facility, then the fact it appeared near a specific BSL facility shouldn't be leading you to the sort of answer you got.

roenxi 7y ago

Well, I'm not qualified to explain this so I'm probably wrong in the detail, but a sketch of the thinking: P(Came from WIV|Global Epidemic starts in Wuhan) ~= 97% However, P(Started Near a BSL Rated facility|Global Epidemic) is also high (not going to estimate it). But you have assumed that P(Global Epidemic starts in Wuhan) = 1; which is not true. P(Global Epidemic starts in Wuhan) is probably quite low and they got unlucky because it had to start somewhere. In this context, that assumption is tantamount to flipping a coin then saying "P(Heads) = 1". It isn't, P(Head) = 0.5 but it does happen sometimes. If we assume P(Global Epidemic starts in Wuhan) = 1 (because it did happen) then P(Came from WIV) is either 0 or 1, because it either did or didn't happen in the same way that the virus started in Wuhan.

dlubarov 7y ago
Hm, you're making sense otherwise but I just don't see where I assumed P(Global Epidemic starts in Wuhan) = 1 -- could you elaborate on that?
- roenxi 7y ago
  Probably not; no. The best I can come up with is that probability is very sensitive to what you assume is happening to generate results. In this case, you're assuming that the WIV in particular is important which I suspect links the pandemic implicitly to Wuhan. That isn't a math error, but it is not going to give you a useful result. This isn't an error of logic so much as an error in scenario construction - it is ignoring possibility that the virus appeared near a random BSL rated facility, which is probably very high since a new virus would likely be detected first in dense urban centers where that sort of infrastructure tends to be. If the virus is likely to appear near a BSL facility, then the fact it appeared near a specific BSL facility shouldn't be leading you to the sort of answer you got.