4 ms·
> Multiply the number above by 1,024 (assumes a doubling of cases every 3 days) if you assume no social distancing measure are put in place: 2.1MM on the low en
by creato 7y ago
> Multiply the number above by 1,024 (assumes a doubling of cases every 3 days) if you assume no social distancing measure are put in place: 2.1MM on the low end, mulitplying by a 10x ratio. (Just because if I multiply by a 50x ratio, it returns a number larger than the 7.8MM total residents in the Bay area.)
This is why the spread of a virus like this is a logistic curve, not an exponential. An exponential is a good model at first, but extrapolating too far doesn't work like this.
- ignoramous 7y ago> This is why the spread of a virus like this is a logistic curve, not an exponential. More on this by 3Blue1Brown: https://www.youtube-nocookie.com/embed/Kas0tIxDvrg https://www.youtube-nocookie.com/embed/Kas0tIxDvrg
- hef19898 7y agoSomewhere after, or around, thee 5 minute mark: "true exponentials are basically non-existent in real life"
- gbrown 7y agoThe reality is even more complicated - sure, a logistic curve is a reasonable fit if we assume that the data is accurate and the population homogeneous and well mixed, but in practice things get more complicated quickly. There's a huge network of potential contacts, with a large degree of heterogeneity and important subcomponents at multiple geographic scales. In addition, the network is dynamic, not static, so that both highly granular and population scale phenomena can change the contact distribution. Two important questions are: 1. What can we actually measure with confidence to relate to a model of interest 2. At what level of sophistication is it feasible to actually model things Neither question is particularly straightforward in the face of ongoing epidemics.
- fsh 7y agoThe data from China almost perfectly follows a logistic curve. Unfortunately, extrapolating such a smooth function is pretty much impossible before it starts saturating anyway.
- gbrown 7y agoFor sure, but the problem is that innumerable true situations might give rise to a given "observed" logistic curve - something that you can describe with two parameters arose from a mix of incomprehensibly complex transmission dynamics and dauntingly difficult (and often hidden) observation mechanisms. The result is that, even though after the fact we can often achieve a good fit with simple models, there's little reason to expect that simple models would have been generally predictive - the feedback loop even includes the models, since they might inform public health policy! This isn't to say that modelling isn't useful, but that forecasting a novel infection while it's ongoing is really, really, really hard. Edit: Also, I’d be interested to see a comparison of the fit between a typical logistic, four parameter logistic, Gompertz etc. Not all sigmoids are the same.
- AstralStorm 7y agoGompertz type 2 fits somewhat better. Ultimately for such complex things like spread with barriers Tsalis statistics are good. That could mean q-Weibull distribution.
- AstralStorm 7y agoNot even remotely: 1) Number of cases is not flat. Even by now. 2) There was a slowed growth in late cases. It fits Weibull statistics. Late spread is random but responds to distance. (A'la Rayleigh.)
- hef19898 7y agoFinally! I have been almost killed for calling this out. It's like some people believe epidemiologists haven't figured that out yet. And it does make a huge difference, whether the underlying function has a natural peak or not.
- baq 7y agoyou're technically right, but i think from a policy making standpoint it doesn't matter because it's the exponential part that needs to be contained by policy and not the saturation part. this is where the hard decisions have to be made. if no decisions are made, saturation starts to happen when the game is lost.